Teratogenic effects of amitraz, 2,4-dimethylaniline, and paraquat on developing frog (Xenopus) embryos.

Developmental effects of amitraz (acaricide), its metabolite (2,4-dimethylaniline), and paraquat (herbicide) on embryos of a nontarget organism, Xenopus laevis, were investigated. Following the standard protocol of the American Society for Testing and Materials (ASTM), the experiments were carried out using native Xenopus frogs. There was a drastic increase in mortality from 24 h to 96 h for paraquat, but 2,4-dimethylaniline showed no mortality at the highest concentration tested (100 mg/L). The 96-h LC(50) values were 0.67, 3.27, and >>100 mg/L for paraquat, amitraz, and 2,4-dimethylaniline, respectively. At concentrations higher than 0.2 mg/L of paraquat all the embryos were malformed, whereas growth reduction was apparent at all test concentrations (0.1-5 mg/L). The most common teratogenic effects were flexures of the notochord and stunting of growth. Edema was the most common effect of amitraz on the embryos, and 100% of the surviving embryos in 5 mg/L were edematous. The 96-h EC(50) (malformation) values were 1.21 (95% CI 0.48-3.03) and 0.18 (95% CI 0.16-0.20) mg/L for amitraz and paraquat, respectively. The ratio of 96-h LC(50) to 96-h EC(50) (malformation), i.e., the teratogenicity index (TI) were 2.7 and 3.72 for amitraz and paraquat, respectively, and for 2,4-dimethylaniline (TI > 5) all the embryos in 25 mg/L showed observable pigment loss and encephalomegaly. This shows that paraquat and the degradation product of amitraz, 2,4-dimethylaniline, should be classified as teratogens. Teratogenic risks of massive application of these pesticides on Kenyan farms should therefore be considered.

Accumulation of metals and histopathology in Oreochromis niloticus exposed to treated NNPC Kaduna (Nigeria) petroleum refinery effluent.

Accumulation of heavy metals and histopathology were observed in Oreochromis niloticus exposed to treated petroleum refinery effluent from the Nigerian National Petroleum Corporation, Kaduna. Analysis of fish metal burden showed that the fish concentrated trace metals a thousand times above the levels existing in the exposure medium. Some metals were preferentially accumulated more than others and the accumulation was, in decreasing order, Pb, Fe, Zn, Cu, Mn, Cr, Ni, and Cd. Whole fish metal burden was lower in fish from which the gill, liver, and kidney had been removed, suggesting that these organs accumulated the metals more than other tissues. Hemorrhaging of fins was observed in all treatment concentrations except that of the control, and fish exposed to 40 and 50% effluent were most affected. Erosion of the caudal fin was also observed in fish exposed to 40 and 50% effluent. Examination of the organs for histopathology revealed damages to the gills. Gills with edematous fused lamellae congested with blood were observed. No histopathological damage was observed in the liver and kidney. The extent of metal accumulation and histopathological damage were directly related to the effluent concentrations.

An arsenic-binding protein in rainbow trout.

A pulse dose of 5 microCi 74As-labeled arsenic acid was given in diet contained in No. 4 gelatin capsules to two groups of rainbow trout (90 +/- 6 g). These groups consisted of the control and the treatment group which was preexposed to 22.8 mg As/kg diet for 2 weeks. An extract of cytosol prepared from the liver of both control and pretreated fish sacrificed 48 hr after the pulse dose was found to contain an arsenic-binding protein with molecular weight of about 19,000. This protein accounted for less than 25% of the extracted cytosol in both the control and preexposed fish. Arsenic may not induce the synthesis of thionein in the liver as the molecular weight of 19,000 is outside the range previously reported for metallothionein. The binding of arsenic to this protein may not be of any adaptive significance.