Knowledge on the biotic and abiotic degradation of chemicals is essential to assess their environmental fate and is a key factor in risk assessment and their registration. While the main focus lies on screening tests to assess biodegradation for industrial chemicals, extensive degradation tests are needed to investigate the route and rate of degradation of agrochemicals. Generally, the degradation of chemicals in soil results in the formation of degradation products (i.e. metabolites), non-extractable residues (NER), microbial biomass and finally in their mineralization. Whereas degradation products and mineralization are relatively easy to assess, identify and evaluate in laboratory tests nature, identity and composition of NER is often unknown. Therefore, the question arises when NER should be considered a risk and when not. Major concerns of NER are the potential bioavailability as well as the release from soil over the long term. Therefore, NER are an important parameter not only in risk assessment (i.e. PEC/PNEC) but also in hazard/persistence assessment (PBT) of chemicals. With regard to EU regulatory aspects of NER there are generally two essentially different views. Firstly, a precautionary approach in the regulation of industrial chemicals considering residues as non-degraded parent which generally overestimates the exposure concentration. Secondly, a more conservative approach within the regulation of agrochemicals considering NER as degraded residues of the active substance which are of no further concern. Herein only a general cut-off criterion is laid down regarding the maximum amount of NER formed in combination with a low mineralization rate. On basis of the nature and definitions of NER in soil the evaluation of NER in environmental risk assessment and PBT assessment within the regulatory context will be discussed. The focus will be laid on agrochemicals considering new findings of the recent past (e.g. biogenic NER) and their possible effects for regulation.

Non-extractable residues of agrochemicals in soil in the regulatory context

256th National Meeting (2018)

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