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Ecotoxicological information

Toxicity to soil microorganisms

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Description of key information

In the reliable (RL 2) nitrogen mineralisation test available, after 28 days no significant effects on nitrogen transformation rate were observed at all tested concentrations up to 1000 mg/kg soil dw. Taking an increase of of respiration and dehydrogenase activity as an adverse effect (most probably not the case and caused by enhanced mineralization of DEHP), the definite long-term NOEC for soil microorganisms is 300 mg/kg soil dw.

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:
300 mg/kg soil dw

Additional information

For this endpoint only two studies are available.

The more recent one was asked by the European Council for Plasticisers and Intermediates in 2000 and comprises three tests following three parameters that are used in the present assessment in a weight of evidence approach.

In this study (ECPI, 2000) possible effects of DEHP on soil micro flora activity (measured as respiration), dehydrogenase activity, and nitrogen materialisation was investigated. Two soils, differing in organic contents (2.3 and 5.9% respectively) and particle size distribution were tested. DEHP at concentrations 0, 10, 30, 100, 300 and 1,000 mg /kg dwt was tested in the respiration and dehydrogenase activity tests (ECPI, 2000b part II and III), while the DEHP concentrations in the nitrogen materialisation test were 0, 30, 300, 600 and 1000 mg/kg dwt (ECPI, 2000a, part I)..

In the nitrogen mineralisation test, recovery rates in DEHP were between 85% and 117% which were regarded as satisfactory and whatever the soil tested, no significant effects were observed at all tested concentrations.

In the respiration and dehydrogenase activity test, recovery rates between the two soils and parameters were quite variable with, in particular, very low recoveries (10 -40%) in soil with low organic content. This indicates that biodegradation of DEHP during the experiment was higher in soil with low organic content than in soil with high organic content. It is also in this first type of soil that a significant increase of respiration and dehydrogenase activity was observed at the highest concentration tested (1000 mg/kg dw). However this effect cannot be considered as negative as it may reflect the increased biological activity due to biodegradation of DEHP. In any case, at the second highest concentration, i.e. 300 mg/kg soil dw, no significantly increased respiration and dehydrogenase activity was observed also for soil of low organic carbon content. Thus, even taking an increase of respiration and dehydrogenase activity as an adverse effect, 300 mg/kg soil dw may be definitely regarded as a NOEC.

Considering these three parameters that show no adverse effect even at the highest concentration tested, it can reasonably be assumed that DEHP does not induce hazardous effect on soil microorganisms. Taking also an increase of respiration and dehydrogenase activity as an adverse effect (discussed in EU RAR, 2008), the definite long-term NOEC for soil microorganisms is 300 mg/kg.

This conclusion is supported by the study of Kirchmann et al. (1991) where up to 250 mg/kg no effects were observed on soil biological processes (respiration, nitrogen mineralisation and, nitrification).