Advances in the development of procedures to establish the toxicity of non-extractable residues (NER) in soil. LRI-ECO25

There is already a long discussion around the bioavailability and ecotoxicological relevance of Non Extractable Residues (NER) in soil. Is NER formation a detoxification process or should it be considered a hidden hazard? NER can only be established using labelled chemicals (e.g. 14C) and cannot be measured with conventional chemical analytics. Regulations ask for understandable and measurable parameters. Considered in the developed tool are three measurable parameters: 1) Chemical present in the water phase, 2) A potentially available fraction in equilibrium with the water phase. 3) The total extractable amount. NER is considered, but mentioned as non-measurable and non-bioavailable. The fates of three NER-forming chemicals were followed in a period of 6 months after addition also using 14C chemicals. For the chemical Tri-NitroToluene (TNT), NER-formation was reproducible and NER formation during aging removed toxicity. By removing the bioavailable fractions directly after spiking and after aging it was also possible to remove toxicity. The experiments showed that toxicity was caused by the bioavailable chemical and not by NER. With Cypermethrin and Carbendazim, results were less clear, because there was a large uncertainty in NER-formation. The degree of biodegradation was not reproducible for Cypermethrin and unexpected losses occurred with Carbendazim and it is not possible to draw conclusions from only a non-labelled experiments.