Arsenic accumulation, tolerance and genotypic variation in plants on arsenical mine wastes in S.W. England

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Abstract
Mine and smelter wastes in S.W.England, containing high concentrations of arsenic and other elements have been investigated. Several soil profiles were examined in detail for water soluble and ‘total’ arsenic, copper and iron levels. Macroelement and pH values were also obtained. The spoil material was highly acidic, deficient in macro‐elements and contained elevated levels of arsenic and iron. Concentrations of water soluble extracts of both arsenic and iron increased markedly down the profile. The conditions have given rise to a specialized arsenic‐tolerant flora which is both impoverished and restricted. Plant cover is generally less than 1 per cent on the very toxic areas. Plants present on the sites include Agrostis tenuis, Agrostis stolonifera, Agrostis canina and Jasione montana. These species were found to accumulate arsenic to high concentrations which, in some cases, approached 1 per cent dry weight. Clonal material of A. tenuis and A. stolonifera from high arsenic sites exhibited tolerance to the arsenate ion at varying concentrations in solution culture, but not to arsenite. An examination of water‐soluble extracts of soil, by a covalent hydride generation technique coupled to an atomic absorption spectrophotometer, has shown that arsenate is the predominant form of arsenic in these soils and concentrations can approach 75 μg/g (air dry soil) at depths below 10 cm. Detailed studies of the water‐soluble extracts show that dimethylarsine can be identified in the soils at low concentrations. Acrylamide gel electrophoresis was used to show that extracts of A. tenuis leaves possessed active esterase isoenzymes. Analysis of different plants from the same clone showed that they possessed identical isoenzyme complements whereas plants from different clones sometimes exhibited different patterns. It was concluded that there are separate evolutionary origins for some of the plants. This could be explained “by the heterogeneity of the chemical and physical conditions at the sites on which these plants have evolved.