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LETHAL AND SUBLETHAL EFFECTS GENERAL As discussed later, most authorities agree on 10 points: (1) inorganic arsenicals are more toxic than organic arsenicals, and trivalent forms are more toxic than pentavalent forms; (2) episodes of arsenic poisoning are either acute or subacute--cases of chronic arsenosis are rarely encountered, except in humans; (3) early developmental stages are the most sensitive to arsenic; (415 inorganic arsenic can traverse placental barriers--as little as 1.7 mg As /kg body weight at critical stages of hamster embryogenesis, for example, can produce fetal death and malformation; (5) biomethylation is the preferred detoxification mechanism for inorganic arsenicals; (6) arsenic is bioconcentrated by organisms, but not biomagnified in the food chain; (7) depressed crop yields were recorded at 3 to 28 mg of water soluble soil As/l, or about 25 to 85 mg total As/kg soil--adversi effects on vegetation were recorded at concentrations in air >3.9 ug As/m ; (8) some aquatic species were adversely affected at water concentrations of 19 to 48 ug As/1, or 120 mg As/kg in the diet, or tissue residues of 1.3 to 5 mg As/kg fresh weight; (9) sensitive species of birds died following single oral doses of 17.4 to 47.6 mg As/kg body weight; and (10) adverse effects were noted in mammals at single oral doses of 2.5 to 33 mg As/kg body weight, at chronic oral doses of 1 to 10 mg As/kg body weight, and at feeding levels of 50 mg, sometimes only 5 mg, As/kg in the diet. It is emphasized in the literature that arsenic metabolism and toxicity vary greatly between species, and that effects are significantly altered by numerous physical, chemical, and biological modifiers. Adverse health effects, for example, may involve respiratory, gastrointestinal, cardiovascular, and hematopoietic systems, and may range from reversible effects to cancer and death, depending partly on the physical and chemical forms of arsenic tested, the route of administration, and dose. CARCINOGENESIS, MUTAGENESIS, AND TERATOGENESIS Epidemiological studies show that increased risk of cancers in skin, lung, liver, lymph, and hematopoietic systems of humans is associated with exposure to inorganic arsenicals. These increased cancer risks are especially prevalent among smelter workers and in those engaged in the production ind use of arsenical pesticides where atmospheric levels exceed 54.6 ug As/m (NRCC 37