Evaluation of biodegradation of nonylphenol ethoxylate and lignin by combining toxicity assessment and chemical characterization.

The aerobic biodegradation of commercial nonylphenol ethoxylate (NPE) mixture and alkali lignin was studied using the OECD headspace test accompanied by the simultaneous measurement of ecotoxicity directly from the biodegradation liquors and by the follow-up of the chemical composition of the studied chemicals. NPE degradation was dependent on the inoculum source: approximately 40% of NPE was mineralized into CO(2) during the 4-week experiment when inoculum from Helsinki City wastewater treatment plant (WWTP) was used, and only 12% was mineralized when inoculum from Jyväskylä City WWTP was used. Chemical analyses revealed a shift in the ethoxylate chain length from longer to shorter soon after the beginning of the NPE biodegradation tests. At the same time also toxicity (reverse electron transport assay, RET) and estrogenic activity (human estrogen receptor yeast) measured directly from the biodegradation liquors decreased. In case of alkali lignin, approximately 11% was mineralized in the test and chemical analysis showed in maximum a 30% decrease in lignin concentration. Toxicity of lignin biodegradation liquors started to decrease in the beginning of the test, but became more toxic towards the end of the test again. Especially RET assay proved to be sensitive enough for measuring toxicity changes directly from biodegradation liquors, although a concentrating treatment of the liquors is recommended for a more detailed characterization and identification of toxic metabolites.

Effects of different plant protection programs on soil microbes.

The aim of this study was to assess the effects of two pesticide regimens (conventional full insurance compared with supervised and reduced pesticide use) and two cultivation techniques (conventional tillage and fertilization compared with no tillage and lower fertilization) on soil microbes in a field study, and to evaluate the results with laboratory tests. The herbicides used were chlorsulfuron, MCPA, and bentazone; the fungicides carboxin-imazalin and propiconazole; and the insecticides dimethoate and pirimicarb. In the field studies, the effects on microbial biota were assessed by measuring biomass (ATP content) and microbial activities related to carbon and nitrogen metabolism (soil respiration, nitrification potential). Potential harmful effects of commercial formulations of the same pesticides on microbes were studied in the laboratory with two bacterial toxicity tests (Pseudomonas putida growth inhibition and Vibrio fischeri luminescence inhibition tests) and with a soil respiration inhibition test. Bioavailability of the pesticides in the soil was assessed by a solid-phase modification of the luminescent bacteria test. In the field studies the microbial activities and biomass followed the weather conditions during the growing season, and significant effects of pesticide treatments on microbial processes were not observed. In the laboratory studies the toxicity of certain pesticides was clearly detected by bacterial toxicity tests. However, in the soil respiration inhibition assessment with soil similar to that used in the field trial, inhibition was observed only at unrealistically high concentrations. This could be due to the limited bioavailability of the pesticides in soil of high clay and organic carbon content.