Consumption-related heavy metal emissions

In the case of the heavy metals Ag, As, Cd, Cr. Cu. Hg, Pb, and Zn, we have found that there are ten categories of consumption that are readily distinguishable in terms of their different degrees of dissipation in use and different modes of release to the environment. These are as follows:

1. Metallic uses, e.g. in alloys. Environmental losses occur mainly in the production stage (discussed previously) and as a result of corrosion in use or discharge to landfills.

2. Plating and surface treatment (excluding paints and pigments) generate some losses in the platings or treatment process and some corrosion losses as above.

3. Paints and pigments generate losses at the point of application and from weathering and wear. Some are ultimately disposed of (e.g. in landfills) along with discarded objects or building materials.

4. Batteries and electronic devices have relatively short useful lives of 1-10 years. Production losses can be significant. Most are discarded to landfills.

5. Other electrical equipment as above, but may be longer-lived.

6. Industrial chemicals and reagents (e.g. catalysts, solvents, etc.) not embodied in products have short useful lives; catalysts and solvents are usually recycled, others are lost directly to air or water.

7. Chemical additives to consumer products include fuel additives, rubber vulcanizing agents and pigments, detergents, plasticizers, photographic film, etc. They are disposed of mainly to landfill or incinerators.

8. Agricultural pesticides, fungicides and herbicides are used dissipatively, on farms, nurseries, etc. Most are immobilized by soil or biologically degraded and volatilized. There is some uptake into the food chain and some amount of loss via run-off.

9. Non-agricultural biocides include the above, as used in homes and gardens, for termite control, etc. These uses are dissipative but most biocides are immobilized by soil, as above.

10. Pharmaceuticals, germicides, etc., are used in the home or in healthservice facilities and are largely discharged via sewage or to incinerators.

More detailed discussion of intermediate and final uses of each metal can be found in the Appendix that follows this chapter.

Table 8 Consumption-related emmissions factors (ppm)

a. As alloys or analgams (in the case of Hg) not used in plating, electrical equipment, catalysts or dental work. Losses can be assumed to be due primarily to wear and corrosion, except for mercury which volatilizes.

b. Protective surfaces deposited by dip coating (e.g. galvanizing, electroplating vacuum deposition, or chemical bath (e.g. chromic acid). The processes in question generally resulted in significant waterborne wastes until the 1970s. Cadmium-plating processes were particularly inefficient until recently (see discussion in Ayres et al., 1988, vol. II). Losses in use are mainly due to wear and abrasion (e.g. silverplate), or flaking (decorative chrome trim). In the case of mercury-tin "silver" for mirrors, losses were largely due to volatilization.

c. Paints and pigments are lost primarily by weathering (e.g. for metal-protecting paints), by wear, or by disposal of painted dyes or pigmented objects, such as magazines. Copper- and mercury-based paints slowly volatilize over time. A factor of 0.5 is rather arbitrarily assumed for all other paints and pigments.

d. Includes all metals and chemicals (e.g. phosphorus) in tubes and primary and secondary batteries, but excludes copper wire. Losses in manufacturing may be significant. Mercury in mercury vapour lamps can escape to the air when tubes are broken. In all other cases it is assumed that discarded equipment goes mainly to landfills. Minor amounts are volatilized in fires or incinerators or lost by corrosion; lead-acid batteries are recycled.

e. Includes solders, contacts, semiconductors and other special materials (but not copper wire) used in electrical equipment control devices. instruments, etc. Losses to the environment are primarily via discard of obsolete equipment to landfills. Mercury used in instruments is lost via breakage and volatilization or spillage.

f. Chemical uses not embodied in final products include catalysts. solvents, reagents, bleaches, etc. In some cases a chemical is basically embodied but there are some losses in processing. Losses in chemical manufacturing per se are included here. Major examples include copper and mercury catalysts (especially in chloride mfg); copper, zinc and chromium as mordants for dyes; mercury losses in felt manufacturing; chromium losses in tanning; lead in desulphurization of gasoline; zinc in rayon spinning, etc. In some cases virtually all of the material is actually dissipated. We include detonators such as mercury fulminate and lead azide (and explosives) in this category.

g. Chemical uses embodied in final products other than paints or batteries include fuel additives (e.g. TEL). anti-corrosion agents (e.g. zinc dithiophosphate), initiators and plasticizers for plastics (e.g. zinc oxide), etc. Also included are wood preservatives and chromium salts embodied in leather. Losses to the environment occur when the embodying productivity is utilized, for example gasoline containing TEL is burned and largely (0.75) dispersed into the atmosphere. However, copper, chromium, and arsenic are used as wood preservatives and and dispersed only if the wood is later burned or incinerated. In the case of silver (photographic film), we assume that 60 per cent is later recovered.

h. Agricultural pesticides, herbicides, and fungicides. Uses are dissipative but heavy metals are largely immobilized by soil. Arsenic and mercury are exceptions because of their volatility.

i. Non-agricultural biocides are the same compounds, used in industrial, commercial, or residential applications. Loss rates are high in some cases.

j. Medical/dental uses are primarily pharmaceutical (including cosmetics) germicides, also dental filling material. Most are dissipated to the environment via waste water. Silver and mercury dental fillings are likely to be buried with the dead body.