No abstract

Accurate knowledge about factors and conditions determining copper (Cu) toxicity in soil is needed for predicting plant growth in various Cu-contaminated soils. Therefore, effects of Cu on growth (biomass production) of lettuce (Lactuca sativa) were tested on seven selected, very different soils spiked with Cu and aged for 2 months at 35 °C. Cu toxicity was expressed as pEC50(Cu(2+)), i.e., the negative logarithm of the EC50(Cu(2+)) activity to plant growth. The determined pEC50(Cu(2+)) was significantly and positively correlated with both the analytically readily available soil pH and concentration of dissolved organic carbon [DOC] which together could explain 87% of the pEC50(Cu(2+)) variation according to the simple equation: pEC50(Cu(2+)) = 0.98 × pH + 345 × [DOC] - 0.27. Other soil characteristics, including the base cation concentrations (Na(+), K(+), Ca(2+), Mg(2+)), the cation exchange capacity at soil pH (ECEC), and at pH 7 (CEC7), soil organic carbon, clay content, and electric conductivity as well as the distribution coefficient (Kd) calculated as the ratio between total soil Cu and water-extractable Cu did not correlate significantly with pEC50(Cu(2+)). Consequently, Cu toxicity, expressed as the negative log of the Cu(2+) activity, to plant growth increases at increasing pH and DOC, which needs to be considered in future management of plant growth on Cu-contaminated soils. The developed regression equation allows identification of soil types in which the phytotoxicity potential of Cu is highest.

Purpose Determination of the ecotoxicity effect factor (EF) in life cycle impact assessment (LCIA) is based on test data reporting the total dissolved concentration of a substance. In spite of the recognised influence of chemical speciation and physico-chemical characteristics of the aquatic systems on toxicity of dissolved metals, these properties are not considered when calculating characterization factors (CFs) for metals. It is hypothesised that the main cause of the variation in reported EC50 values of Cu among published test results lies in different speciation patterns for Cu in the test media, and that the toxicity of Cu is predominantly caused by the free Cu 2+ ion. Hence, the free Cu 2+ ion concentration should substitute the total dissolved metal concentration when determining the EF. Materials and methods The study was based on a review of published ecotoxicity studies reporting acute and chronic EC50 data for Cu to Daphnia magna and to different species of fish and algae. The speciation pattern of Cu in the different media applied in the studies was calculated using the Visual MINTEQ model. EFs were calculated according to the expression applied in the USEtox™ characterization model. Results and discussionReported EC 50 values for Cu show variations of one to several orders of magnitude for the same organism, but the study indicates that the large variation is caused by differences in water chemistry of the test media influencing the metal speciation. The relationship between the calculated free Cu 2+ ion concentration and reported EC 50 values indicates that the aquatic ecotoxicity of Cu to D. magna can be predicted from the free ion concentration. Other results confirm that the free Cu 2+ ion concentration depends on the [Cu]/[DOC] ratio since the majority of the total dissolved Cu is present as Cu-DOC complexes when the media contains more than 1 mg/L of DOC, and since Cu in such complexes has limited availability to the test organisms. Conclusions These results suggest that speciation should be taken into account in the modelling of both EFs and fate factors for LCIA, and the EF for Cu in the aquatic environment should be based on the concentration of the free Cu 2+ ion.