Biogenic formation of non-extractable residues from pesticides in soil
Zusammenfassung der Projektergebnisse
We determined the turnover mass balances of 13C3^15N-glyphosate (13C3^15N-GLY), 13C6-metamitron (13C6-MTR) and C10^15N-bentazone (C10^15N-BTZ) in soil and water-sediment systems. This general mass balance based on 13C and or 15N-labelling technique was extended to biomolecule analyses (fatty acids and amino acids). By amino acid analysis we calculated the extent of 13C and or 15N-label incorporation into microbial biomass and ultimately estimated the total content of biogenic non-extractable residues (bioNER) formation. Major formation of bioNER was relevant for the readily biodegradable compounds GLY and MTR displaying high mineralisation rates. In contrast to GLY and MTR, only small amounts of bioNER were formed from the more recalcitrant compound BTZ suggesting that for xenobiotics with a low mineralisation potential, xenobiotic NER dominate the total NER. BioNER in soil or sediments can be formed under different metabolic conditions. Our studies showed that bioNER from 13C3^15N-GLY were formed during both active metabolism and starvation, whereas bioNER from 13C6-MTR were mainly formed under active metabolism. 15N-bioNER from 15N-GLY in water-sediment system were formed mainly during the active metabolism, whereas in soil 15N-bioNER were formed during both active and starvation metabolism. We could prove for the first time that the sarcosine pathway is relevant in the degradation of this pesticide in both soil and water-sediment. The sarcosine pathway has not been previously documented for terrestrial systems; also in our experiments it was more pronouced in the water-sediment system. Xenobiotic parent compounds and / or their metabolites may be sequestered in or covalently bound to the soil matrix ultimately forming xenobiotic NER (Bollag et al., 1992) of type I with high release potential and/or type II with little or no release potential. However, during degradation of either natural or xenobiotic organic compounds, microorganisms use the compounds as carbon and nitrogen sources to build up their biomass components; after cell death and lysis their cell constituents will be incorporated into the non-living organic matter (OM) of soil and sediment, and stabilised ultimately forming hardly extractable bioNER (type III). Contrary to xenobiotic NER, bioNER are only composed of nontoxic microbial components stabilised in the OM. They do not pose any risk for the environment or public health and lead to an overestimation of the general risk related to NER in soil or sediment. GLY and MTR explicitly formed bioNER with no risk (type III). In contrast to GLY and MTR, the NER formed during turnover of BTZ are mostly xenobiotic either of type I with high risk or type II with low risk for the environment or public health. Therefore, individual assessment of the NER formation from all compounds is necessary.
Projektbezogene Publikationen (Auswahl)
-
Classification and modelling of nonextractable residue (NER) formation of xenobiotics in soil – a synthesis. 2014. Crit. Rev. Environ. Sci. Technol., 44, 2107–2171
Kästner, M.; Nowak, K.M.; Miltner, A.; Trapp, S; Schäffer, A.
-
(Bio)degradation of glyphosate in water-sediment microcosms – A stable isotope co-labeling approach. Water Research, Volume 99, 1 August 2016, Pages 91-100
Wang, S; Seiwert, B.; Kästner, M.; Miltner, A.; Schäffer, A.; Reemtsma, T.; Yang, Qi; Nowak, K.M.
