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The toxicity of 13 anilines and 11 phenols to Daphnia magna has been assessed at pH values of 6.0, 7.8, and 9.0. Toxicity of anilines decreases with decreasing pH, whereas the toxicity of phenols decreases with increasing pH. These variations in toxicity, are clearly brought about by the effect of ionization, especially for the phenols. Toxicity decreased with an increasing proportion of ionized molecules. The relative contribution of the ionized and unionized molecules was assessed. It is believed that, at least for the phenols, the ionized form of the compounds does contribute to the toxicity of the molecules. However, the decreased overall toxicity suggests that a lower relative toxicity is attributable to the ionized form. Attempts were also made to develop quantitative structure‐activity relationship (QSAR) models for these toxicity data. Reasonable QSARs were produced for the anilines and phenols, acting as polar narcotics, considered together; these QSARs included a measure of hydrophobicity, pKa, and hydrogen bonding. When the phenols and anilines were considered separately, better, hydrophobicity‐based, QSARs were obtained. Most compounds, with the exception of 2,4‐dinitrophenol, resorcinol, and pentachlorophenol, were thought to be acting by a polar narcosis mechanism of toxic action. There was some evidence that 2,4‐dichlorophenol and 2,4,6‐trichlorophenol may be acting as weak acid respiratory uncouplers, despite earlier suggestions that they act as polar narcotics. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 140–148, 2000

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In order to identify the effects of soil properties on the transfer of Cd from soil to wheat under actual field conditions, 126 pairs of topsoil and wheat samples were collected from the Yangtze River delta region, China. Relevant parameters (Cd, Ca, Mg, Fe, Mn, Zn, N, P, K, S, pH, total organic carbon, and speciation of soil Cd) in soil and wheat tissues were analyzed, and the results were treated by statistical methods. Soil samples (19.8%) and 14.3% of the wheat grain samples exceeded the relevant maximum permissible Cd concentrations in China for agricultural soil and wheat grain, respectively. The major speciations of Cd in soil were exchangeable, bound to carbonates and fulvic and humic acid fraction, and they were readily affected by soil pH, total Ca, Mg, S and P, DTPA-Fe, Ex-Ca, and Ex-Mg. Cadmium showed a strong correlation with Fe, S, and P present in the grain and the soil, whereas there was no significant correlation in the straw or root. Generally, soil pH, Ca, Mg, Mn, P, and slowly available K restricted Cd transfer from soil to wheat, whereas soil S, N, Zn, DTPA-Fe, and total organic carbon enhance Cd uptake by wheat.

The chemical speciation of nine heavy metals in intertidal sediments from Quanzhou Bay was determined using a modified sequential extraction procedure, proposed by the Commission of the European Community Bureau of Reference. The results show that Mn presents the highest percentage in the acid-soluble fraction, and Pb and Cu present the highest percentages in the reducible fraction. The highest percentages of Fe, V, Cr, Ni, Zn, and Co were found in the residual fraction. The mobility order of the heavy metals studied on the basis of the nonresidual content of the elements is Mn > Pb > Cu > Co > Zn > Ni > Cr > V > Fe. The assessment on potential ecological risk indices of some heavy metals indicates that Zn, Ni, and Cr show moderate contamination, while Cu and Pb show slighter contamination. On the whole, the comprehensive potential ecological risk index of Cu, Zn, Ni, Cr, and Pb in the sediments presents moderate degree.

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In Central Sweden an estimated 80% of the lakes contain fish exceeding health guidelines for mercury. This area overlaps extensively with the Bergslagen ore region, where intensive mining of iron ores and massive sulfide ores occurred over the past millennium. Although only a few mines still operate today, thousands of mineral occurrences and mining sites are documented in the region. Here, we present data on long-term mercury pollution in 16 sediment records from 15 lakes, which indicate that direct release of mercury to lakes and watercourses was already significant prior to industrialization (

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