In standard soil toxicity tests, heavy metals are amended as water-soluble salts. The role of the counterion in metal salt toxicity is scarcely looked into. In this study, we assessed the contribution of nitrate and chloride to the toxicity of lead to Folsomia candida in a natural standard soil. Both lead salts were tested according the standard test protocol as well as after percolation of the soil with deionized water. Lead nitrate was more toxic than lead chloride for survival as well as reproduction. Percolation proved to be an effective method to remove counterions from the soil. Survival of F. candida increased for both metal salts when percolation was included. Percolation reduced the reproduction toxicity of lead, the effect of which was largest for the nitrate salt. In percolated treatments, the nitrate and chloride lead salts did not differ in toxicity. It is concluded that counterions contribute to metal toxicity and that nitrate is more toxic to F. candida than chloride.

To compare the effectiveness of acute and chronic bioassays for the ecological risk assessment of polluted soils, soil samples from a site with an historical mineral oil contamination (< 50-3,300 mg oil/kg dry soil) at the Petroleum Harbour in Amsterdam, The Netherlands, were screened for ecological effects using acute and chronic bioassays. A two-step 0.001 M Ca(NO3)2 extraction at a final solution-to-soil ratio of 1:1 was used to prepare extracts for the acute bioassays. Acute bioassays (< or = 5 d) applied to the 0.001 M Ca(NO3)2 extracts from the polluted and reference soils included growth tests with bacteria (Bacillus sp.), algae (Raphidocelis subcapitata), and plants (Lactuca sativa), immobility tests with nematodes (Plectus acuminatus), springtails (Folsomia candida), and cladocerans (Daphnia magna), and the Microtox test (Vibrio fischeri). Chronic bioassays (four weeks) performed on the same soil samples included tests with L. sativa, F. candida, and earthworms (Eisenia fetida) and the bait-lamina test (substrate consumption). The acute bioassays on Microtox showed a response that corresponded with the level of oil pollution. All other acute bioassays did not show such a consistent response, probably because pollutant levels were too low to cause acute effects. All chronic bioassays showed sublethal responses according to the contaminant levels (oil and in some soils also metals). This shows that chronic bioassays on soil samples are more sensitive in assessing the toxicity of mineral oil contamination in soil than acute bioassays on soil extracts. A pilot scale bioremediation study on soils taken from the two most polluted sites and a control site showed a rapid decline of oil concentrations to reach a stable level within eight weeks. Acute bioassays applied to the soils, using Microtox, algae, and D. magna, and chronic bioassays, using plants, Collembola, earthworms, and bait-lamina consumption, in all cases showed a rapid reduction of toxicity, which could be attributed to the degradation of light oil fractions.

To compare the effectiveness of acute and chronic bioassays for the ecological risk assessment of polluted soils, soil samples from a site with an historical mineral oil contamination (< 50-3,300 mg oil/kg dry soil) at the Petroleum Harbour in Amsterdam, The Netherlands, were screened for ecological effects using acute and chronic bioassays. A two-step 0.001 M Ca(NO3)2 extraction at a final solution-to-soil ratio of 1:1 was used to prepare extracts for the acute bioassays. Acute bioassays (< or = 5 d) applied to the 0.001 M Ca(NO3)2 extracts from the polluted and reference soils included growth tests with bacteria (Bacillus sp.), algae (Raphidocelis subcapitata), and plants (Lactuca sativa), immobility tests with nematodes (Plectus acuminatus), springtails (Folsomia candida), and cladocerans (Daphnia magna), and the Microtox test (Vibrio fischeri). Chronic bioassays (four weeks) performed on the same soil samples included tests with L. sativa, F. candida, and earthworms (Eisenia fetida) and the bait-lamina test (substrate consumption). The acute bioassays on Microtox showed a response that corresponded with the level of oil pollution. All other acute bioassays did not show such a consistent response, probably because pollutant levels were too low to cause acute effects. All chronic bioassays showed sublethal responses according to the contaminant levels (oil and in some soils also metals). This shows that chronic bioassays on soil samples are more sensitive in assessing the toxicity of mineral oil contamination in soil than acute bioassays on soil extracts. A pilot scale bioremediation study on soils taken from the two most polluted sites and a control site showed a rapid decline of oil concentrations to reach a stable level within eight weeks. Acute bioassays applied to the soils, using Microtox, algae, and D. magna, and chronic bioassays, using plants, Collembola, earthworms, and bait-lamina consumption, in all cases showed a rapid reduction of toxicity, which could be attributed to the degradation of light oil fractions.