A correlation between the fate and non-extractable residue formation of¹⁴C-metalaxyl and enzymatic activities in soil

Abstract

Extracellular, oxidative soil enzymes like monophenol oxidases and peroxidases play an important role in transformation of xenobiotics and the formation of organic matter in soil. Additionally, these enzymes may be involved in the formation of non-extractable residues (NERs) of xenobiotics during humification processes. To examine this correlation, the fate of the fungicide (14)C metalaxyl in soil samples from Ultuna (Sweden) was studied. Using different soil sterilization techniques, it was possible to differentiate between free, immobilized, and abiotic ("pseudoenzyme"-like) oxidative activities. A correlation between the formation of metalaxyl NER and soil organic matter content, biotic activities, as well as extracellular phenoloxidase and peroxidase activities in the bulk soil and its particle size fractions was determined. Extracellular soil-bound enzymes were involved in NER formation (up to 8% of applied radioactivity after 92 days) of the fungicide independently from the presence of living microbes and different distributions of the NER in the soil humic subfractions.

Bacterial Preferences for Specific Soil Particle Size Fractions Revealed by Community Analyses

“…Considering their characteristic surface properties and associated microenvironments, different PSFs most likely select for specifically adapted microbial entities in soil. Previous studies have revealed PSF-specific microbial activity, as indicated by measurements of soil enzymes (Stemmer et al, 1998 ; Kandeler et al, 2000 ; Marx et al, 2005 ), nitrogen mineralization, ammonification, nitrification and denitrification (Lensi et al, 1995 ; Nacro et al, 1996 ; Christensen and Olesen, 1998 ), methanogenesis (Zhang et al, 2007 ; Zheng et al, 2007 ), and sorption and mineralization of organic pollutants (Botterweck et al, 2014 ; Hemkemeyer et al, 2015 ). Furthermore, the abundance of a gene involved in phosphorous-cycling differed between PSFs (Luo et al, 2017 ).…”