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TESTING STRATEGIES
during the test as this would lead to an underestimation of the toxicity. To limit such desorption
an adequate equilibration period before the start of the test is recommended. In addition the
actual concentration of the test substance in the sediment should be monitored at least at the
beginning and at the end of the test to check the efficiency of the contamination technique and
the stability of the test substance concentration.
6.3.4 Soil compartment
At an initial stage and in respect to the current proceedings in the aquatic compartment, a
minimum data set for risk assessment for soil organisms could be based on short-term toxic
effects data. PECsoil/PNECsoil ratios are derived from either ecotoxicological data or the
equilibrium partitioning method (see Section 3.6.2.).
Two cases can be identified where it might be considered necessary to revise the PNECsoil,:
(1) short-term tests on primary producers, consumers and decomposers should be performed if
the equilibrium partitioning method is applied because of the absence of toxicity data for
soil organisms and the PECsoil/PNECsoil is > 1. In some cases long-term tests might be
preferred immediately when, for example, soil organisms or part of the life-cycle of a plant
or microbial processes are suspected to be particularly sensitive to the test compound. This
is especially true, if the substance in question exhibits a log Kow greater than 5 (equivalent
to a log Koc > 4) or exhibits a corresponding binding behaviour;
(2) further testing may be necessary if the PNECsoil is based on toxicity data for soil organisms
using assessment factors and the PEC/PNECsoil > 1. Long-term tests should be considered in
particular if the available PNECsoil is based on short-term effects. Depending on the effect
that a substance has on vascular plants, earthworms or processes mediated by
microorganisms, the information about the effect on the most sensitive organisms has to be
improved by conducting appropriate tests for the respective endpoints. The choice of the test
species will be made on a case-by-case basis taking into account the availability of a suitable
test method, the sensitivity of aquatic and/or sediment living organisms that may be
predictable for the sensitivity of equivalent groups of soil organisms, the indicative nature of
the assessment factors and the uncertainty in the proposed approach.
Internationally accepted methods (OECD and ISO) should preferably be used but results from
other methods that are in the process of being standardised might also be appropriate. Several
research programmes have been initiated that are aimed at the development of soil tests: the
Netherlands Integrated Soil Research Programme (NISRP; Eijsackers, 1989) and the Swedish
Mark Test System (MATS; Rundgren et al., 1989). More recently, ten European laboratories
have formed a network (SECOFASE, Løkke and van Gestel, 1993) funded by the European
Union to develop, improve and standardize tests systems for assessing sublethal effects of
chemicals on fauna in soil ecosystems. As a result of this European research project, test
protocols, indications on species sensitivities, reproducibility of the tests and also advice for the
choice of test species has been published in the “Handbook of soil invertebrate toxicity tests”
(Løkke and van Gestel, 1998).
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