|Initial Environmental Assessment: Plant Protection - Series no 13 (NORAD, 1995)|
|Part I: General account|
Chemical pesticides are synthetically produced compounds to control various kinds of unwanted organisms - weeds, fungi, mites, insects etc. In this booklet, such organisms will collectively be referred to as pests.
Plant diseases resulting in reduced crops is a common problem in agriculture. When chemical pesticides were introduced in the 1940s they were regarded as a major achievement. Pesticides were introduced in the developing countries as part of "the green revolution" where the objective was a growth in agricultural production. The pesticides were relatively inexpensive and highly effective, and soon it became common practice to spray all crops regularly throughout the growing season, even when there were no visible signs of diseases. Since then, the considerable environmental impacts of pesticides which may occur have become apparent. We also know that pesticides often lose some of their effect when used for long periods of time. Many pests have become resistant to pesticides and are therefore very difficult to control.
These observations have lead to increased efforts to find alternative pest management methods to chemical pesticides. One of the alternatives, the so-called IPM, or Integrated Pest Management, has gained considerable attention.
However, it does seem unlikely that all use of pesticides will end in the future. New methods and regulations for the secure use of pesticides are constantly being developed, encouraged by a number of international regulations and recommendations. One prominent example is the collaboration between FAO and WHO on plant protection management. These two organisations have compiled a list of the maximum pesticide residue limit of various nutrients. FAD/WHO Codex Alimentarious Commission is an international forum for food safety. The Commission concerns itself with industrial pollution, additives, heavy metals, mycotoxines, pesticide residues and other xenobiotics in nutrients. A special committee, the "Codex Committee on Pesticide Residues" determines the so-called Maximum Residue Limit for pesticides in nutrients. The residue limits set by the Codex Committee have been accepted in most countries.
Yet another example of international regulations and recommendations is the 1985 FAO conference, where an "International Code of Conduct on Distribution and Use of Pesticides" was passed. The background for this was the fact that many developing countries lack an infrastructure for pesticide approval. This is the reason why FAO gives priority to national programmes for pesticide control, which will result in better security for the persons handling the spraying, as well as for the consumers.
Countries which do not have a pesticide control agency, will have to rely on the importing agencies with regard to safe distribution and use of pesticides. In some cases, pesticides which no longer have official approval in developed countries are still being distributed in developing countries. This must be stopped. The safe use of pesticides requires knowledge about official approval and distribution as well as storage and the application of the pesticides. Many developing countries lack an administrative agency to select relevant pesticides, as well as sufficient training of personnel to handle them. This situation makes safe handling and use of pesticides more difficult.
This booklet emphasises a description of possible environmental impacts from the use of pesticides. However, alternative nonchemical agents will also be considered. The main focus is on agricultural plant protection, and the use of pesticides in other contexts is dealt with only very briefly.
Some of the most common pests are virus, bacteria, fungi, insects, nematode and rodents.
Weeds may be defined as "unwanted plants". This means that no plants are originally defined as weeds. A plant becomes a weed when it no longer is wanted where it grows. A large number of plants may be described as weeds. Plants which are usually regarded as cultivated plants may in some situations be defined as weeds, for example when contaminating seed production. Weeds compete with cultivated plants for water, light and nourishment. The result may be reduced crops of poorer quality. This can happen when inhibited growth of cultivated plants occurs, or when weeds harvested together with the cultivated plants affect the flavour or are toxic. As so many plant species may be defined as weeds, a large number of biological characteristics may be involved. Many common weeds in field crops are annual. They germinate from seed, grow rapidly and set new seeds prior to or at the same time as the cultivated plant. In addition to propagation by seeds these species also have an advanced system of vegetative propagation, such as budding from the root system. Weeds of this kind are highly competitive and are particularly difficult to control.
Plant diseases can also damage cultivated plants. Plant diseases can be caused by virus, bacteria and fungi. However, lack of nutrients and poisoning may produce many of the same symptoms as plant diseases.
Virus propagate in plants and are transmitted from plant to plant. The most common symptoms of a virus disease are mosaic, leaf blotch, chlorosis, yellowing leaves, and necrocytosis of tissue, leaves, tubers and other parts of the plants. Virus may also be transmitted by vegetative propagation, or by nematode, mites, aphids, leafhoppers and certain other insects transmitting virus from plant to plant.
Bacteria cause rot in tubers, fruits, bulbs and other succulent plant organs. Some bacteria grow in the tissue and may cause blight. Bacteria are transmitted by seed, tubers and by vegetative propagation.
Fungi are the cause of most plant diseases. They produce microscopic spores which are transmitted by wind and plant material. Some species survive in the soil and are transmitted via the plants' root systems. Fungi can kill sprouts, cause root rot, rot in tubers, blights and blotches. Some fungi produce mycotoxines in the plant products. Mycotoxines are poisonous to both humans and farms animals.
Pests. All animal species have their function in the ecosystem. An ecosystem is an interactive community of plants, animals, micro-organisms with the environment which they inhabit, which together make up a functional whole. To put it simply: No humans, no pests. Pests on plants can be defined as follows: "A pest is a species whose population density exceeds an acceptable level and which causes financial damage to the crop". In addition, there are pests on stored nutrients and species which directly or indirectly cause serious diseases in both humans and animals. The most common pests belong to the following groups of animals: insects, mites, nematoda, birds and rodents. Insects constitute about 75% of all defined species. An estimate suggests about 4-5 million insect species. About two thirds live in the tropics. About 1000 insect species are considered major pests on cultivated plants, and an estimated 30.000 are minor pests. In tropical and subtropical areas, particularly in areas with only minor seasonal changes in temperature and precipitation, one insect species may have more generations per year than in temperate climates. The insect population may increase rapidly in the case of a continuous access to host plants. Some phytophagous insect species are very omnivorous, but many important insect pests specialise on one plant family and have highly effective mechanisms to find host plants. Traditional tillage systems in the tropics, such as the intercropping of two or more cultivated plants, may interfere with such mechanisms and reduce insect attacks on the cultivated plants. Monocultures, where a single crop is cultivated year after year in large areas, may be highly vulnerable to attacks from specialised insect pests. All pests have many natural enemies. Utility animals may be categorised as predators and parasites. Some predators attack many species, whereas others tend to be more specific. Parasites are specialised. The female ichneumon wasp, for example, lay eggs inside the host animal. The larvae lives inside the host animal and ultimately kills it.
1.3.1 Use of chemical pesticides
Projects and activities connected to the use of pesticides can generally be categorised as follows:
· Ordinary measures: This may include measures related to agriculture, forestry, animal husbandry, fisheries, aquaculture, where pesticides are used to increase production or reduce losses in the field or in storage. The use of pesticides may be repeated at different times or at different phases of the production to prevent damage to crops and products.
· Extraordinary measures: These include measures to control particular pests and weeds. Generally this means extraordinary or isolated measures. Examples are special measures to control migratory grasshoppers, or to prevent the spread of diseases to humans (for example malaria), or measures taken to remove unwanted vegetation by various development programmes, such as the construction of transport arteries.
· Technical, professional and financial improvement of institutions and authorities to ensure training of personnel and secure the use and management of pesticides.
Projects and measures may also include research and legislation.
Choice of technology and type of project may vary depending on the activity where the use of pesticides is involved, on the type of weed or pest to be controlled, as well as on local environmental, economic, technological, institutional and socio-economic conditions. Experience shows that the conditions in many developing countries may require other kinds of solutions than those being practiced in industrialised countries.
1.3.2 The use of non-chemical plant protection agents
Projects and activities in this category may include biological control agents and preventive measures, and can be categorised as follows:
· Practical organisation: This includes the organization of biological control methods, including IPM (Integrated Pest Management). Such measures can be the planning of IPM projects in co-operation with the users, or the training of personnel.
· Support to regional plant protection organisations: Such organisations can co-ordinate lists of weeds and pests defines as hazardous, quarantine arrangements and other plant protection measures.
· Research and development, which can include the development of cultivated plants which will be resistant to common diseases and pests, or improve the understanding of how the elements in the local agro-economical system interact.
The many types of chemical pesticides can be very different and are used in different contexts. There is a sliding transition between the definitions of preservatives, medicines and pesticides. In this booklet, only pesticides distributed in the environment to control pests will be described.
Pesticides are organised according to what category of organisms they are used against. They can be categorised as follows:
Herbicides - against weeds.
Fungicides - against fungi.
Insecticides - against insects.
Acaricides- against mites.
Nematicides - against nematode.
Rodenticides - against rodents.
Although each category of pesticide is intended for a particular group of weeds or pests, one should be aware that most chemical pesticides can have a varying degree of poisonous effect on other types of organism than the one the pesticide was intended for. The significance of the natural enemies of insect pests has been stressed in integrated protection management (IPM) projects (see ch. 1.5). The most important natural enemies are other insects, and comprehensive insecticides will often have an equally strong effect on the utility insects as on the insect pest. Experience shows that fungicides and herbicides can have a negative effect on the natural enemies of insects. In Table 4 at the end of this booklet, an attempt has been made to show the toxicity of the most important groups of pesticides to the natural enemies of insect pests.
All chemical pesticides are more or less poisonous and can cause health damage. Depending how harmful they are to humans and farm animals, they have been classified in one of the follwing toxicity groups:
Toxicity group X = Highly toxic compound.
Toxicity group A =Toxic compound.
Toxicity group B = The compound can seriously damage your health.
Toxicity group C = The compound can cause some damage to your health.
Tables 1-3 at the end of this booklet offer an outline of the
toxicity groups of various fungicides, insecticides and herbicides.
The chemical pesticides can be classified into several main groups, based on their chemical structure and biochemical reactivity mechanisms. Chlorinated hydrocarbons (DDT and others) were very common compounds in the earliest pesticides, but such compounds have now been banned in most countries because of slow degradation and a disruptive effect on the food chain. Chlorinated hydrocarbons were replaced by organic phosphor pesticides. Synthetic pyretroids are yet another, more recent, group of pesticides.
Pesticides can be used in the following situations:
· Cultivated plants:
- To spray cultivated plants to protect against attacks from fungi, insects and mites etc. This will be of particular importance in monocultures, and for export products (cotton, fruit etc.).
- To use herbicides to attenuate or kill rival plants (weeds) which inhibit the growth of the cultivated plants.
- Remove unwanted vegetation prior to bringing new crops into cultivation.
· Seed: Seed treatment to protect against insects, fungi in the soil or fungi which can be transmitted by seed.
· Accumulation of pest organisms:
Spraying of such organisms, for example to control migratory grasshoppers.
· Other situations: Spraying water sources to improve visibility, passability etc. Chemical control of water plants can be required to improve conditions for fishing or transport. Spraying to remove unwanted vegetation in connection with right-of-way (ROW) clearance for power lines etc. Routine control of the vegetation or weeds along roadsides etc.
Some chemical compounds are not used for plant protection, but in the following situations:
· Farm animals: To kill ectoparasites on farm animals by bathing them in so-called cattle dips in a pesticide solution (see booklet No.2, "Animal husbandry").
· Products in storage: To spray agricultural products, fish products etc. in order to protect them during storage.
· Living conditions for intermediate hosts:
Spraying water sources or vegetation areas which serve as propagation areas or habitats for intermediary hosts for diseases, such as anopheles, tsetse flies or bilharzia snails etc.
Pesticides come in bags, tins, bottles or cans, in the form of powder, granulate or liquid. Commercial products of pesticides can have different pesticide concentrations in different formulae and compounds, depending on the intended area of use.
Transport: Pesticides are often transported by vans, lorries etc. which are also used for the transport of cereal products, farm animals or nutrients. This requires thorough cleaning of the storage area after use to remove all traces of the pesticide.
Storing the pesticide: Pesticides are usually bought in a highly concentrated form, and they can therefore be very poisonous. For this reason, they should always be stored in a secure and lockable storage space with strictly controlled access.
Dilution and piling up: The commercial product can in some cases be used directly for dusting or fumigation, but usually the product must be diluted and sprayed. When diluting the pesticide or filling the diluted liquid into the spraying receptacle, large quantities of the pesticide can spill out. It is therefore of utmost importance that the user has good equipment, solid routines and access to a well suited area for diluting the pesticide and filling it into the receptacle.
Spraying the pesticide: The spraying equipment can be hand sprayers, knapsack sprayers, tractor sprayers and sprayers on aeroplanes or helicopters. The latter entail the greatest risk for spraying areas which do not require treatment. Pesticides can also be added to the irrigation water or the water sources. It is important that the spraying equipment and spraying routines are satisfactory to ensure that the pesticide is used in correct quantities and only in the desired areas. Incorrectly adjusted spraying equipment can easily result in overdosage.
Systematic control and supervision of the treated area can be an important step in reducing the need for pesticide spraying. It will then be easier to discover diseases and instigate measures against diseases or insect pests at an earlier stage and thus reduce losses and the need for spraying.
Pesticide wastes and cleaning the spraying equipment can cause acute pollution. Secure routines for handling pesticide wastes are essential. The agricultural methods can affect the use of pesticides. Balanced fertilisation and rotation of crops can reduce the frequency and extent of diseases. If, however, there is one-sided use of for example nitrogen fertilisers, or if the same crop is cultivated year after year, the need for pesticides may increase.
The conditions in each developing country must be taken into account when using pesticides. One must consider whether only specially trained personnel should be given the responsibility and control of the pesticides, or whether they can be handled by the local population. Furthermore, one must check whether there exists a pesticide control agency in the country. In cases where the farmer carries out the pesticide spraying himself, it is necessary to consider the availability of different kinds of spraying equipment and protective equipment before selecting the pesticide.
For thousands of years plants have been cultivated without the use of chemical pesticides. Today many attempts are being made to find alternatives to pesticides in order to have environmentally safe plant protection.
Biological control of pests involve the use of living organisms, including virus and natural enemies. This includes the use of predators, parasitoids (organisms with a parasitic mode of life and which ultimately kill their hosts), pathogenes (organisms which cause communicable diseases) and antagonists (organisms which can defeat pests or keep them at a low level). The organisms used for biological control are first and foremost insects, mites, nematode, fungi, bacteria and virus; in other words the same categories of organisms one usually attempts to control. Using insect pheromones to catch large numbers or to confuse pest behaviour is also an aspect of biological control methods.
Integrated pest management - IPM. In addition to using other organisms and natural hosts, integrated pest management also involves other methods to hinder pests, for example using cultivated plants which are not affected or only slightly affected by harmful organisms. The aim is to control pests and diseases, not to exterminate them. Several methods can be combined, such as the use of pesticides, mechanical measures, manual methods etc. When using chemicals in such programmes, the pesticide must be carefully selected (with regard to selectivity, effect on natural enemies etc.), and used in as small quantities as possible. An important aspect is the prospective financial loss: How extensive must the pest attack be for the use of pesticide to be economically justifiable? If the attack is not very widespread, the pesticide treatment will cost more than the estimated profit from the crop. By IPM the different methods can interact and give a better total result than if only one agent was being used.
Resistance: Different cultivated plant species have different tolerance levels of pests and plant diseases. Systematic plant breeding has given crops which are resistant to diseases or pests. Some species of wheat, for example, have become resistant to black stem rust and other fungal diseases. Some species of rice have been bred to become resistant to pest insects and virus, and to the fungus Pyricularia oryzae. For the farmer, resistance is a simple and inexpensive plant protection method. Seed manufacturers collect information about the resistance of different seeds. The International Agricultural Research Centres, with support from the Consultative Group on International Agriculture (CGIAR) have focused on resistance when breeding species for tropical and subtropical climates.
Non-infectious plant material: Insects, mites, nematode, fungi, bacteria and virus can accompany seeds, seed potatoes, scions, cuttings and other propagation material. Setting up a control agency to ensure that seeds and all propagation materials are noninfectious is therefore of great importance. It is especially important when importing seeds from other countries and parts of the world (see booklet No.1 "Agriculture").
Quarantine: Most countries have compiled lists of pests, virus, bacteria and fungi which do not exist in their country. Importing countries should always obtain documented proof that the seed imported is non-infectious. Other measures to avoid importing pests are inspection on arrival and growing in quarantine. Inspection routines and growing in quarantine are generally poor in developing countries. Banning all import of seeds from certain cultivated plants can be a possible measure, but such a ban requires strict control. There are numerous examples of pests spreading rapidly from one country to another soon after having entered the continent. A rust fungus on maize was imported to West-Africa in 1949, and in the course of just five years it had spread to all parts of the continent as well as to Madagascar. Another example is coffee rust, which is of African origin. When discovered in Brazil in 1970, measures were taken to exterminate it. The attempts were unsuccessful, and there is now coffee rust in all coffee producing countries in South and Central America.
Regional plant protection organisations: To avoid the spreading of pests, regional organisations have been established to coordinate lists of hazardous pests, quarantine regulations and other measures against spreading. Some such organisations are the FAO Caribbean Plant Protection Commission, the European Plant Protection Organisation, the Inter-African Phytosanitary Commission, the FAO Near East Plant Protection Commission, and the FAO Plant Protection Committee for Southeast Asia and Pacific Region.
A number of natural environmental conditions can be important for the prospective environmental impacts of pesticides. Some are listed below.
Geology and soil conditions: Information concerning types of soil in the pesticide treatment area can often be important. The composition and nature of the soil can be of great importance with regard to the speed of pesticide degradation and to the speed with which it will be transported through the soil.
Hydrological and hydro-geological conditions: Water may carry pesticides to the surrounding area and be a significant unintended recipient for pesticides. Large amount of precipitation over short periods of time can carry pesticides to surrounding areas. Information about expected precipitation during the spraying period is important. One should also have gained information about the direction in which the precipitation flows on the ground, and about water recipients in surrounding areas, such as ground water, brooks, rivers and dams.
The topography is often decisive with regard to what extent and in what direction wind and water may carry pesticides. Topographical conditions can for example lead pesticides to nearby brooks and lakes during heavy rainfall.
Climate: The health conditions of flora and fauna are closely related to climactic factors such as temperature, humidity and precipitation. This is also true of pests. Great seasonal variations, as in temperate climates, reduce the diversity of species, and lead to fewer pests with short life cycles. Consequently, it is relatively simple to find out at what point the organisms will be most vulnerable, and thus when to start pest control. In warmer climates, however, the breeding season for pests is more continuous, and corresponding measures must be taken to control them. Consequently, pesticides may be used too frequently. In areas with small climactic variations, constantly high temperatures and unvarying humidity, pest organisms may have many generations every year. The reproduction is potentially enormous as long as there is sufficient nourishment. This can cause serious fungi and insect problems in many food production and storage areas. A hot climate can also cause rapid evaporation of pesticides, which means that they can be spread to the atmosphere and transported across large areas. Wind can transport pesticides across great distances, either in liquid form or with soil particles. It is therefore of utmost importance to have information concerning the wind conditions in the area during periods of spraying or dusting (see chapter 3.1).
Vulnerable ecosystems and rare species can be affected by pesticides, directly or indirectly. Information about the existence of vulnerable ecosystems and rare species in the surrounding area is important. Such information can affect the choice of type and dosage of pesticide, and the point of time to implement the pesticide treatment.
Employment conditions: Agriculture dependent on pesticides are generally less labour-demanding than agriculture which do not make use of such agents. Consequently, information about the extent to which the employment situation depends on the use of pesticides in agriculture is required. Will women be especially affected by a prospective change?
In many developing countries, the institutional conditions connected to plant protection and the use of pesticides are insufficient. Often, the country lacks an agency which can examine the use and character of the pesticide in relation to local environmental conditions, as well as institutions to give official approval to pesticides based on such examinations. Such institutions are also needed to adjust the directions for use to local conditions. If such institutions are lacking, one has to rely on information from other countries. When that is the case, the information should preferably come from countries with similar climactic conditions. Sufficient knowledge about chemical pesticides is often lacking. In particular, some users have very little information about possible environmental impacts and health risks related to the use of pesticides. Users may in some cases be unable to understand the directions because of illiteracy. This can be a serious obstacle to the effective and secure handling of chemical pesticides.
Lack of waste management systems after spraying, can be a problem in many places. Pesticide waste is classified as hazardous waste, and requires special handling (see booklet No.11 "Waste management").
The local pollution situation: It is generally assumed that natural environmental conditions have certain tolerance limits. Certain amounts of pollution can be absorbed in nature without causing significant changes in the ecosystem in the area. However, if the tolerance limit is exceeded, the ecosystem may change so that some species will decline while others will increase. If one is to estimate the project's prospective risk of exceeding the tolerance limit, information about the prospective dosages of pesticide is required, as well as about the extent of annual pollution from other sources in the area, and the extent of already existing pollution. In addition, one must decide the acceptable upper limit of pesticide in the drinking water to avoid it becoming a health hazard for humans and animals.
This survey considers both direct and indirect environmental impacts. It can often be difficult to distinguish clearly between these two types of impacts. The causes of direct impacts can be linked directly to certain characteristics of the project in question. Indirect impacts can result from other types of activities associated with the project, such as trade and transport, or if the project affects socio-cultural conditions in the local community.
This survey also presents recommendations for mitigative measures that can reduce prospective environmental impacts.
a) Wind drift after pesticide treatment: The drift or spreading of pesticides by air will vary significantly depending on the type of equipment and method used, the wind force, the form of pesticide used (liquid, emulsion or dust), the height of the spray nozles, the size of drops or particles, the evaporation of the pesticide, temperature and humidity.
The equipment and method used: When spraying a field by hand sprayers, knapsack sprayers and tractor sprayers, there are generally few problems with unintended spraying. When such equipment is used correctly, the liquid spray can be controlled very well - the deviation is normally only about one metre. However, when the pesticide is sprayed from an aeroplane or a helicopter, the area of spraying is considerably less precise.
Wind force: Low wind force is of great importance to minimise the risk of wind drift. Strong wind can result in significant spreading of the pesticide spray. It can, however, be difficult to find a precise definition of "low wind force". It is recommended that the wind is within the limits of calm to light air (0-1 knots) or slight breeze (4-6 knots) on Beaufort's wind scale. A more precise definition of acceptable wind force must rely on the other conditions mentioned in this chapter.
The form of pesticide used: The extent of wind drift will also depend on the form of pesticide used (liquid, emulsion or dust). Spraying 1-2 metres above ground will result in a wind drift of a few hundred metres for particles, and up to one kilometre for drops, and several kilometres for gas.
The size of drops or particles: Small drops or particles are carried by wind more easily than large drops. The size of drops is significant for at least two different reasons: First of all, large drops fall to the ground more quickly than small drops. From a height of 80 cm, which is the most common boom height for spraying, a drop of 10 nanometres takes 4.5 minutes to hit the ground. If the size of the drops is multiplied by ten, the drops take only 2.5 seconds to hit the ground. Second, the size of drops affects the evaporation of the pesticide liquid. The smaller the drops, the faster the evaporation. In certain conditions (a temperature of 20° Celsius and a relative humidity of 80% ) drops of 100 nanometres will evaporate completely in 57 seconds. If the drop size is halved and other conditions remain the same, it will only take 14 seconds for a drop to evaporate.
Height of fall: The spraying quality depends to a great extent on the height of the nozzle above ground. The higher above ground, the larger quantities may be spread by wind to surrounding areas. The height of fall, and consequently, the wind drift, is greatest by aeroplane or helicopter spraying.
The evaporation of the pesticide: Different types of pesticides evaporate from liquid to gas form at different points. Pesticides in gas form are transported by the wind much more easily than pesticides in liquid form. Some kinds of pesticides evaporate quickly, while others take longer.
Temperature and humidity: Temperature and humidity conditions affect the evaporation speed of pesticide drops. The higher the temperature and the lower the humidity, the more will evaporate. Drops of 50 nanometres will evaporate in 14 seconds if the temperature is 20° Celsius and if the relative humidity is 80 %. However, if the temperature changes to 30° and the relative humidity to 50%, drops of the same size will evaporate in just 4 seconds.
It is important to note that the above factors must be viewed collectively before estimating the unintended spreading of the pesticide to surrounding areas. The effect from unintended spreading of chemical pesticides on humans, animals and vegetation depends on the toxicity of the pesticide, and on the extent to which it comes into direct contact with the organism.
b) Spreading by evaporation: Pesticides can evaporate after reaching the ground. Consequently, they can rise to high air strata and be transported across enormous distances. This has happened with DDT, linden, dieldrin and other stabile components, remnants of which can be found in lake sediments, ocean sediments and aquatic organisms. The extent of evaporation depends not only on the already mentioned conditions for evaporation from spraying, but also on the pesticide binding to soil particles, and on its water solubility. Evaporation will be reduced if the pesticide is subjected to soil incoporation.
c) Spreading by soil particles: Pesticides are often bound to soil particles, which in turn can be transported by the wind. This is particularly true in areas where the soil is dry and light. Research has show that particles larger than a diameter of 0.06 mm are only transported a few metres by air. Particles larger than 0.02 mm fall relatively quickly to the ground after having been transported by the wind. Smaller particles can be transported across very great distances.
d) Mitigative measures: The following mitigative measures can be useful to reduce the risk of unintended spreading of pesticides by air:
· There should be no pesticide spraying in strong winds.
· When possible, spraying from aeroplane and helicopter should be avoided, and should as a rule never be done in the proximity of housing areas.
· Spraying upwind of housing areas should be avoided.
· The spray nozzle should be as close to the ground as possible.
· Pesticide drops should be as large as possible, and mist blowing should be used as seldom as possible.
· Spraying small drops should be avoided in periods with low relative humidity and high temperatures.
· Preference should be given to pesticides which do not evaporate easily.
As a result of regular spraying, pesticides inevitably will come into contact with the soil. This is also the case when pesticides are emptied or spilled on the field, in watercourses or in other places. Such direct discharges can cause particularly high and acute pesticide concentrations. What follows below is an outline of how pesticides can be spread to surrounding areas by surface water, or by being transported by the water through the soil, or by the root systems of plants, before ultimately being released into the soil.
a) Surface leaching: Plant protection agents generally have the same leaching pattern as nutrients and soil particles. The leaching pattern can vary from year to year, from place to place, and depends on weather conditions, topography and the nature of the soil.
Sorption to soil particles. The degree of the pesticide's sorption to soil particles depends both on the pesticide and the nature of the soil. Pesticides with strong sorption to soil particles are especially likely to be transported by surface water. This usually occurs immediately after heavy rainfall, and can result in pesticidic ponds in low-lying areas, or in polluted brooks and rivers.
Soil preparation: The extent of soil preparation usually has an effect on the surface transport of pesticides. Less soil preparation reduces the loss of pesticides with strong sorption capacity, which mainly are transported by soil particles. However, the extent of soil preparation has no influence on the loss of pesticides with weak sorption to the soil, since they can be transported easily by surface water without being attached to soil particles.
Soil erosion has an effect on the spreading of pesticides. If there is heavy erosion many soil particles disappear, and along with them the pesticides. Certain methods and the time of soil preparation can increase the risk of erosion. Erosion is often caused by heavy precipitation (see booklet No. 1 "Agriculture" and No. 7, Water supply").
b) Spreading through the soil: The following conditions can affect the pesticide transport through the soil: the chemical nature, drainage and structure of the soil and the root systems of plants.
The chemical nature of the soil: The mobility of the pesticide is affected by its solubility in water and the binding to soil particles - the greater solubility and weaker binding, the greater mobility. A phenoxide such as MPCA is highly soluble, whereas DDT is practically non-soluble. The solubility depends among other things on whether the pesticide is acidic or alkaline. In the tropical climates the soil is generally acidic and contains iron and aluminium oxides (see booklet No.1 "Agriculture"). Kaolinite is the most common clay soil. Kaolinite, oxide and hydroxide are contributing factors to low ion exchange capacity. When this occurs in acidic soils, pesticides with negative or neutral ion charge are easily leached out. The soil in tropical climates generally contains little organic material and clay. This is a highly contributing factor to increasing the mobility of the pesticide or causing it to be leached out of the soil.
The drainage and structure of the soil: The transport of pesticides through the soil also depends on the amount of water in circulation and the saturation capability of the soil. If the soil contains a lot of water, which can occur after heavy rainfall, pesticides will be leached out easily. Pesticides can thus pollute the ground water (see chapter 3.3). The saturation of the soil depends on the amount of cracks, worm holes or old root systems. When there is a surplus of water in the soil, tile drains can also transport water containing pesticides. Both water soluble pesticides as well as pesticides with strong binding to soil particles will be transported through soil profiles with many cracks. However, in compact soil such as clay soil, which is rich in organic materials, it is mainly water soluble pesticides and pesticides with weak binding to soil particles which will be washed out. Soil preparation and a more permanent vegetation surface will prevent the water from flowing downwards and thus reduce the vertical transport of highly soluble pesticides.
Spreading by the root systems: Pesticides can be absorbed by some plants and transported through the plant to the root system where it is subsequently released into the soil. This can happen relatively quickly, but is usually of little importance because only small quantities are being transported.
c) Mitigative measures: The following measures can be taken to hinder unintended transport of pesticides by water:
· To hinder acute discharges by:
- Establishing safe conditions for diluting the pesticide and
filling it on sprayers.
- Establishing safe pesticide handling routines.
- Establishing safe routines for cleaning the spraying equipment.
· Pesticide resits in sprayers may be avoided by diluting a smaller quantity of pesticide than is normally recommended for the last portion, and then using it more sparingly.
· Very poisonous pesticides should not be used on fields sloping down to watercourses during seasons with heavy precipitation.
· The risk of soil erosion and surface flow should be reduced.
· Pesticides with high risk of leaching, such as triazines, should not be used on porous soil above important ground water sources. The ground water then risks being polluted for several decades.
Pesticide residue in water can cause serious pollution, both of ground water as well as of surface water. In most industrialised countries, the criteria for high water quality insist that water should not contain more than 0.1 ppm of any single pesticide, or a total of 0.5 ppm of pesticides. In some watercourses in agricultural areas, there can be concentrations of a single pesticide which far exceed this limit. A heavy rain shower immediately after spraying can result in pesticide pollution of the water, and this can cause the death of fish and also have other ecological impacts. Research shows that concentrations as low as 1 ppm can change biodiversity in the plant plankton in lakes. Before planning pesticide spraying treatment, one must check whether there are important water sources in the area, and if there is a risk of water pollution. (See also chapter 3.2 above.)
A significant portion of the pesticides used will sooner or later be degraded to harmless substances. The faster the pesticide is degraded, the smaller the risk of spreading. The degradation speed depends on a number of factors. Generally speaking, the degradation speed will be reduced by drought, poor supply of nutrients and low temperatures. For every ten-degree drop in temperature the degradation speed is increased 2-4 times. Furthermore, highly soluble pesticides degrade more quickly than non-soluble pesticides, and pesticides with strong binding to soil particles degrade more slowly. It is largely the micro-organisms in the soil which degrade pesticides. Such organisms will be positively affected by the same factors as the cultivated plants. This means that soil preparation, irrigation and fertilisation will accelerate the micro-organisms' degradation of the pesticides.
Toxicologists often stress the half life period as one of the factors affecting the official approval of a pesticide. The half life period is the time required for the degradation of half the pesticide substance. For some pesticides the half life period is several years, for others months, weeks, days or hours. The half life period for one single pesticide can vary significantly, depending on the conditions of the soil mentioned above. For example, the half life period for phenoxide may vary from 4-18 weeks and from 15 years for parathion.
When using pesticides, one should aim at a total degradation of the pesticide by the time the effect of the pesticide treatment has been achieved. This will not only reduce the extent of unintended spreading, but also ensure that farmers have a choice as to what kind of crops they wish to grow next season, unhindered by any pesticide residues from the previous season. If a pesticide has not been degraded by the time there is a drought, active pesticides agents can remain in the soil the following season.
Some mitigative measures:
· Avoid pesticides with slow degradation, particularly if local environmental conditions lengthen the degradation period.
· Avoid that sprayed areas lie fallow. Cultivation increases the degradation speed of pesticides.
The purpose of using pesticides is to protect cultivated plants against pests. When properly used, pesticides will result in good conditions for cultivated plants, while the pests are being controlled. However, pesticides do not only affect pests. Other organisms are also affected, either directly or indirectly. When an organism comes into contact with a pesticide, the pesticide will have a direct effect on the organism, depending on the properties and dosage of the pesticide. A pesticide can also have indirect effects, as when it alters the food chains for organisms.
Accumulation of pesticides in the food chains can often be a serious problem. Accumulation can occur when organisms on one level in the food chain eat organisms on a lower level which contain relatively small concentrations of pesticides. When the animal digests such organisms the pesticide is only partially liberated, and is stored in the body of the animal. In the course of time the animal can gain pesticide concentrations in the body which far exceed the amount in each of the organisms it ate. If such animals are eaten by other animals higher up on the food chain, the same thing will happen again. Thus pesticide concentration will become greater higher up in the food chains. This phenomenon is called bioaccumulation, and it means that the species on the higher levels will be affected the most. In some cases this means humans. The impacts of pesticides accumulated in food chains vary depending on which species are being affected. Pesticides will be stored more readily in some organisms than in others, and the toxicity can vary from one organism to the next. Many phosphorous organic pesticides are very poisonous, have long life span and/or have poisonous decomposition products. Some very poisonous, but highly effective pesticides can pass quickly through the food chain. An example are dying insects eaten by rodents, which in turn will be eaten by birds of prey or predators. The effect can spread across enormous distances and affect stocks of birds and mammals which live and breed far away from the sprayed area, for example as with migratory birds and animals. The impacts can vary significantly. If the pesticide is poisonous to the organism, the organism will decline. It will also decline if the pesticide removes the means of subsistence or diminish the living conditions for the organism in other ways. The reverse will happen if the spreading of the pesticide causes the decimation of rival organisms, or if the pesticide actually becomes an additional nutrient source. The latter is the case for organisms which are able to break down pesticide molecules. Such organisms will subsequently increase in numbers.
Impacts on soil organisms: The soil organisms are important for plants and for animals in the higher levels in the food chains. They produce nutritive substances which the plants can utilise, and can also be food for animals on higher levels in the food chains. The interaction between different kinds of soil organisms is so complex that it is difficult to draw any general conclusions about how they are affected by pesticides. It seems that isolated use of pesticides has no long-term effects on soil processes. However, long-term effects may occur after repeated treatments. But it is not certain whether the total impact is positive or negative.
Plant species living in the areas where the pesticide is used can be affected, for example if bees and other pollinating insects decline, or if the plants are affected in a more direct way. One example is when plant populations defined as weeds are exterminated or kept in strict control in and around the areas exposed to herbicide treatment. This will result in a decline in the total seed setting in the area, which in turn will lead to a decline of the species. The species can often be important in interaction with the ecosystem in the nearby areas. Whenever one species declines, another will usually increase. Herbicides may thus alter the composition of plant species in the area. The use of herbicides may result in the decline of a number of plant species.
Insects: The composition of insects is affected by the predominant plants in the area.
Usually the number of insects will decline when the number of plant species declines. Insects are affected not only by the composition of plant species, but also by the fact that many pesticides have been produced with the intention to kill insects. Insects can be affected by coming into direct contact with the insecticide or by eating other affected insects.
Fish: Fish living in downstream areas subjected to pesticide treatment are often affected. This is particularly the case for fish living in brooks, rivers or small lakes which are fed by areas subjected to pesticide treatment. Sudden discharges can also cause problems.
Birds: According to reports, birds' feathers and bodies are rarely directly exposed to pesticides. However, birds may be affected by eating rodents, worms or insects containing pesticides, or by eating pesticide-treated seeds or pesticides granulates. This can have both acute effects as well as long-term impacts, such as reduced reproduction. Birds for whom insects are an important nutrient source, can be affected if the number of insects decline. Both local as well as migratory birds can be affected by pesticides.
Larger animals can also be harmed by pesticides. For example, herbivores can eat pesticide-treated plants and consequently be affected. Predators can be affected by eating plant-eaters containing pesticides.
When using pesticides in large areas, as for example when spraying against locust swarms and tsetse flies, many other groups of animals will inevitably be affected by the pesticide. Such groups are generally described as Non-Target Organisms. Mainly insects and other anthropodes will be affected in such cases, but other kinds of animals, such as birds, can also be at risk. Species with many different functions in the ecosystem can be affected, including plant-eaters, pollinating insects, predators and parasites. In some cases, rare and vulnerable species can be affected.
The choice of pesticide and type of pesticide treatment is generally difficult. It requires not only information about the impact on the organisms which are to be protected or controlled, but also about the following aspects:
· The degree of acute toxicity to humans and animals.
· Properties which may cause the pesticide to be accumulated and concentrated in the food chains (bioaccumulation).
· The extent to which the degradation speed of the pesticide is affected by different climates and different media (such as water, soil, agricultural products etc.).
· The degree of toxicity to the natural enemies of the pest organism.
· The potential risk of developing resistance to the pesticide.
The following mitigative measures can limit the impacts on flora and fauna:
· Use a pesticide which is highly selective, i.e. attacks only selected species.
· Bioaccumulative and highly poisonous pesticides should not be used in areas where there is any risk of water pollution by transport of sediments by soil erosion or heavy rain, or by wind drift. If that is the case, the pesticide can end up in sediments where it can cause the pollution of fish and other edible animals for several decades in the future.
· If there is an ongoing integrated pest management project in the area, pesticides should be used with caution, to prevent any impacts on biological control agents.
Using reduced doses of pesticides can cause some harm on non-target organisms. One should therefore have sufficient information about whether using reduced pesticide doses can control the pest while at the same time reducing the impacts on the non-target organisms. Research on insecticides used on locusts in Africa has shown that reduced pesticide doses can control the locusts, while the negative impacts on other insects in the ecosystem are being reduced. The doses used were reduced to less than half of the doses recommended by FAO and the manufacturer, but good results depended on the type of pesticide used. More recent pesticides tended to be better than old pesticides. The effect of reduced pesticide doses was better in areas with little vegetation than in areas with dense vegetation.
The health risks of pesticide use include acute poisoning as
well as injuries evolving over time. The spraying personnel can be poisoned by
getting pesticide on the skin or in the respiratory passages. Chronic poisoning
can be the result of long-term exposure to pesticides. The injury can appear a
long time after the exposure to the pesticide. Carcinogenic pesticides are an
example of chronic poisoning. Today, all new pesticides are examined for any
carcinogenic effects, potential foetal injury or mutagenic effects. Pesticides
causing such injuries will not be given official approval.
The following aspects influence the prospective health risk of a pesticide:
· The degree of toxicity when in direct contact with the skin, the digestive organs or the respiratory passages.
· The handling of the pesticide. Whether the pesticide is handled in such a way that it can enter the body.
· The chemical properties of the pesticide, such as solubility in water, fat solubility and acidity, which can be of decisive importance with regard to uptake in or direct contact with the body.
· The immune defence and health condition of the body.
· The use of alcohol, tobacco or other toxicants which can increase the risk of poisoning.
Distribution and storage: Pesticides must be regarded as hazardous toxicants during transport, storage and distribution (see chapter 1.5). Spillage of liquids from cans and spraying powder from broken bags can expose a lot of people to health risks. If the pesticide is stored in rooms with bad ventilation or is placed on shelves in shops, cooperatives or other outlets, pesticide spillage can expose both staff and customers to health risks. Every farmer must keep the pesticides in a securely locked place. In both industrialised countries as well as in developing countries, there have been many accidents where children or others have been exposed to pesticides. In some cases, pesticides have been used for suicides.
Health risks caused by the use of pesticides: Persons involved in pesticide spraying, seed treatment, fumigation or soil disinfection will be exposed to vapour, drops of liquid, dust or fumes from the pesticide. Other persons close to the area where pesticides are weighed or measured before use or who may be in the treatment area, can be exposed. Pesticide residue in insufficiently cleaned packaging materials and spraying equipment can be dangerous for children and others. The concentration of the pesticide is considerably higher before dilution. The inhalation of powder dust or fumes from spraying liquid can therefore be a considerable health hazard. The spillage of concentrated spraying liquid on the skin during dilution can be particularly dangerous. Diluted pesticide can be absorped through skin during the spraying. The skin adsorption can thus take place over a much longer period of time, and the amount of pesticide liquid taken up can be considerable.
Uptake in the body: The most important uptake routes are through the skin and the respiratory passages. Improper handling of pesticides can cause the pesticide to be sprayed into the mouth and thus to be taken up in the lungs or the digestive organs. The extent of skin uptake depends on the fat solubility of the pesticide. Organic phosphor pesticides and chlorinated hydrocarbons are fat soluble and are easily adsorpted through skin. The extent of skin adsorption depends on the solubility products found in the pesticide. Warm and sweaty skin has a higher adsorption than dry skin. When the pesticide has been taken up in the body the blood veins will carry it through the body. Some pesticides can cause local damage to lungs, skin or eyes. Other pesticides can cause damage to internal organs such as the kidneys and the liver.
Symptoms of poisoning: Poisonous compounds disturb the natural biochemical processes in the body. Such processes can tolerate some strain before they are damaged. The body can tolerate small poisonous quantities, but when exposed to bigger doses, the metabolism will be hindered and symptoms of poisoning will appear. There are hundreds of different types of pesticides, and the symptoms of poisoning vary considerably. Common symptoms are headaches, dizziness, limpness, nausea, vomiting, sweat, flow of spit or tears, diminished pupils or visual disorders. In more serious cases there may be chest pains, dyspnea, convulsions, paralysis and unconsciousness.
First aid in the event of poisoning: Any suspicion of poisoning must be regarded as poisoning until there is proof to the contrary. See a doctor or other medical personnel as soon as possible. In the event of serious poisoning the following general first aid measures may be taken:
· Take the patient away from the pesticide area and into fresh air.
· Make sure that the respiratory passages are unobstructed.
· Put the patient in a lateral position.
· Administer artificial respiration if necessary
· Remove polluted clothing. Wash and rinse any parts of the body which may have come into contact with the pesticide. Rinse the eyes with running water.
· If the patient has swallowed poisonous material and is conscious, provoke vomiting. If the patient has been poisoned by strong acids, lye or petroleum distillates, vomiting must not be provoked.
· Call for medical assistance and explain what substance has caused the poisoning.
Protective equipment: The purpose of personal protective equipment is to protect skin, eyes, respiratory passages and the body as a whole against pesticides. As long as clothes are changed frequently, and always in the event of spillages, all-covering cotton overalls can offer equally good protection against skin exposure as clothing made of impregnated materials. Intact, unbroken gloves made of neoprene rubber or PVC plastic offers protection for the hands. It is very important that no pesticide is spilt into the gloves, as this increases the risk of uptake and allergic reactions. A face screen protects the face against sprays when diluting the pesticide. A gas mask or other respiratory protection is required during spraying of the most poisonous pesticides under conditions when there is a lot of wind drift or dusting.
By mist spraying of hazardous pesticides the use of respiratory protection with filters is necessary. Many places may have limited access to advanced protective equipment such as gas masks, but the importance of simple protective equipment such as special clothing, gloves etc. should always be stressed.
Pesticide residues in food and fodder must be avoided. Whenever food is exported on a large scale, the pesticide residue problem must be dealt with in particular. A small number of farmers can destroy major export projects if pesticide residues are detected in the food by the importing country.
The drinking water resources must never be sprayed with pesticides or used for dumping pesticide wastes, or for cleaning the spraying equipment. A protective zone of a minimum of 20 to 50 metres should be established around the drinking water resources, including the tributaries.
For many small farmers pesticides can be an expensive investment in agricultural production. The use of pesticides may lead to debt problems in the event of crop failure caused by other factors than pests, for example drought.
Herbicides in particular can reduce the demand for labour. A considerable part of agricultural labour in the plant production in developing countries is related to weeding. Consequently, a conversion to pesticides may cause higher local unemployment. If there are few alternative jobs in the area, people may move to the bigger cities. Women and men will be affected differently by such changes. Generally speaking, the weeding is the responsibility of women, whereas men handle machinery and other technical equipment. This division of labour can lead to higher unemployment among women then among men if there is a conversion from weeding to the use of herbicides.
No plant is originally a weed. Plants become weeds when we no longer want them. The distinction between weeds and useful plants is consequently unclear and depends on the situation. In developing countries some plants which are usually regarded as weeds are harvested and used for food. In areas treated with herbicides this option is drastically reduced.
The conversion to pesticides can affect other types of agriculture in the area. For example, the use of insecticides can reduce the number of utility insects in the area. This can reduce the crops for farmers who use such insects to control insect pests.
Agruello, Sandramaria Sanchez, 1990: "The utilisation of agrochemicals in Nicaragua and their effect on the environment and human health" NORAD, Managua.
Croft, B.A., 1990: "Arthropod biological control agents and pesticides", Wiley, New York.
Hance, R.J. & Holly, K (eds.), 1990: "Weed Control Handbook: Principles", Blackwell Scientific Publications, Oxford.
Hill, D.S. & Waller, J.M., 1988: "Pests and Diseases of Tropical Crops. Vol. 1-2", Longman, London and New York.
Kreuger, R.F. & Seiber, J. N (eds.), 1984: "Treatment and Disposal of Pesticide Wastes", ACS Symposium series 259, Washington DC.
Thurston, H.D., 1984. "Tropical Plant Diseases" American Phytopathological Society, St.Paul, Minnesota, USA.
The World Bank: "Environmental Assessment Sourcebook. Volume II & III", 1991.