Improvement of the applicability of ecotoxicological tests with earthworms, springtails, and plants for the assessment of metals in natural soils

Abstract

The environmental risk assessment of metals in the soil compartment is based mainly on tests performed in Organization for Economic Cooperation and Development (OECD) artificial soil, but ecologically, the use of natural soils would be more relevant. In this contribution, the reproduction and growth of three standard species (an earthworm, a collembolan, and a dicotyledonous plant, respectively) was evaluated in nine natural soils (covering a wide range of pH values, organic matter content, texture, and so on) and in OECD artificial soil. Afterward, the effects of the model chemical zinc nitrate were assessed in all soils that were identified as being suitable for these species. The test results indicate that the toxicity of zinc nitrate can be higher by a factor of approximately four compared to artificial soil for invertebrates (earthworms and collembolans), whereas plants are only slightly more sensitive in some natural soils than in artificial soil. When comparing the different endpoints, it could be confirmed that the median effective concentration (EC50) is the most robust compared to the highly uncertain 10% effective concentration. Decreasing toxicity of zinc nitrate to collembolans was significantly correlated with an increase in soil pH but not with cation exchange capacity (CEC) or organic carbon (OC) content. No significant correlation was found between the toxicity of zinc nitrate to earthworms or plants and soil pH, CEC, or OC content. Possible consequences of the results are discussed, such as the testing of natural soils in addition to the OECD artificial soil or the inclusion of an additional safety factor to use the EC50 in current risk assessment schemes focusing on no-observed-effect concentrations.

The bait-lamina earthworm test: a possible addition to the chronic earthworm toxicity test?

“…In the case of zinc, this relationship has been substantiated: For the earthworm Eisenia fetida, pH and OM content are most important when tested in a range of artificial soils with different pH values and OM contents (Spurgeon and Hopkin 1996). In the earthworm tests presented here, the correlation between zinc toxicity and soil factors like pH, OC content and CEC was not significant, which might be caused by the fact that the tested soils had very different properties, while in the work cited above only artificial soils with different adjusted pH values and OM contents were tested (Römbke et al 2006a). Therefore, it is not clear whether the availability of zinc indirectly played a role in the effects of zinc on the feeding activity.…”

“…Test vessels were polystyrene cups with a base area of 110 9 155 mm and a height of 60 mm (Bellaplast 590, Polarcup, Alf, Germany). Five concentrations of zinc nitrate were selected according to literature data (Römbke et al 2006a experiment an amount of 5 g food per 500 g soil DW was mixed into the test soil. After the start of the experiment, food was first provided one day after application of the test item and introduction of the adult worms.…”

“…These validity criteria were fulfilled in the controls of all tests with both test substances (Römbke et al 2006a(Römbke et al , 2007. In the case of the bait-lamina field test ISO 18311 (ISO 2016) requires that at Fig.…”

“…In addition, their effects on soil organisms (besides earthworms also springtails) and plants any were already studied in a wide range of soils, including those used in this study (e.g. Römbke et al 2006aRömbke et al , 2007. Especially the latter is known as being toxic for annelids and, in particular, snails (Moore et al 1991;Giusti et al 2013).…”

State of the science and the way forward for the ecotoxicological assessment of contaminated land

“…However, properties of some natural soils could be outside the tolerance thresholds for the soil invertebrate test species used in standardized OECD or ISO tests. Römbke et al (2006b) investigated the performance metrics for some of these species, including E. andrei and F. candida in nine uncontaminated natural soils and OECD artificial soil (Table 2). Their studies revealed that reproduction of the test species varied greatly among the soils and was related to differences in soil properties, including texture, OM content, and soil pH (Figure 1).…”