Ecological effects - trdoer40225

reproductive organs, pancreatic islets, muscle, kidney, liver, and bone. Excretion

of zinc is mainly though the gastrointestinal tract, though some of the zinc is

reabsorbed. It is also excreted via urine, feces, sweat, hair, and saliva. Placental

transfer of zinc may also occur. The half-life of zinc in humans in 200 to

400 days.

Ecological effects

Zinc is an essential micronutrient for all living organisms. Because zinc is

essential, zinc is bioaccumulated by all organisms. The toxicity of zinc is

dependent upon its chemical form and degree of interconversion among the

various forms. Zinc will not be sorbed or bound unless it is dissolved, but bound

zinc will dissolve in the digestive tract following the ingestion of particulates.

The toxicity of undissolved zinc to a particular species depends on the feeding

habits. Aquatic plants and most fish are relatively unaffected by suspended zinc

in the water column. Both terrestrial and aquatic invertebrates and filter feeder

fish might be adversely affected by ingestion of sufficient quantities of

particulates containing zinc. The acute toxicity of zinc to aquatic animals is

influenced by several parameters including increasing hardness, abundant

dissolved oxygen, and low temperatures which lower the potential toxicity of

zinc.

Reported acute toxicity testing for freshwater organisms indicates that insects

are most resistant whereas cladocerans and the striped bass are the most sensitive

to zinc. The reported mean genus acute value for cladoceran is 50.56 ug/l at a

hardness of 50 mg/l. The final acute value representing zinc toxicity to

freshwater species is 108.4 ug/l at a hardness of 50 mg/l.

The range of species mean acute values for saltwater invertebrates extends

from 166 ug/l for embryos of the quahog clams, Mercenaria mercenaria, to

320,400 ug/l for adults of the clam, Macoma balthica. In general, early life stages

of saltwater invertebrates and fish are more sensitive to zinc than juveniles and

adults. The saltwater final acute value for zinc is 174.5 ug/l which is higher than

the acute value of 166 ug/l for the quahog clam. Chronic toxicity values range

from 47 to 852 ug/l and appear to be relatively unaffected by hardness.

Zinc was found to accumulate in freshwater animal tissues from 51 to

1,130 times the concentration present in the water (USEPA 1980). Steady-state

zinc bioconcentration factors for 12 aquatic species range from approximately

4 to 24,000 (USEPA 1980).

Zinc bioconcentration from soil by terrestrial plants, invertebrates, and

mammals, in values of 0.4, 8 and 0.6, have been reported. It has also been

reported that phytotoxic tissue zinc levels ranging from 200 to 400 ppm. Studies

have reported that 60 to 81 ppm of zinc in wheat and corn tissue is phytotoxic.

The tolerance of domestic livestock to zinc in animal feed ranges from 300 to

1,000 ppm (National Academy of Science (NAS) 1980). Zinc poisoning has

occurred in cattle. In one outbreak, poisoning was caused by food accidentally

contaminated with zinc at a concentration of 20 g/kg. An estimated intake of

D73

Appendix D Toxicological Profiles