Effect of oxygen status on pesticide transformation and sorption in undisturbed soil and lake sediment

Abstract

Abstract-The behavior of four chemically distinctly different pesticides (aldicarb, simazine, mecoprop, and phenoxic acid [MCPA] was investigated under simulated redox conditions that occur at the terrestrial-aqueous interface. Sorption was measured in soil and lake sediment and in pure and combined pesticide solutions to study effects of competition. Transformation was investigated in undisturbed soil microcolumns and in anaerobic lake sediment. Using an air-tight nitrogen incubator, oxygen concentrations were varied from 20.8% (ambient) to less then 0.01 % v/v O 2 , while redox potentials varied from ϩ330 to Ϫ120 mV. Aldicarb was transformed more rapidly under anaerobic than under aerobic conditions. Under low oxygen conditions, both reductive and oxidative metabolites were formed. Simazine showed some reductive transformation, but the overall transformation rate decreased with decreasing O 2 concentrations. A pronounced redox effect was shown for both mecoprop and MCPA. With decreasing oxygen concentrations, transformation rates decreased from 0.173 to less than 0.001 d Ϫ1 , monitored over 200 d. These compounds, which are considered improbable leachers based on their short aerobic half lifes, appear to be more persistent in low-oxygenous conditions. It is shown that a period of oxygen inhibition could be survived by the responsible soil microorganisms and was followed by accelerated transformation of the compound when oxygen became abundant again. No relationship was observed between sorption affinity and transformation rate. The effect of redox conditions that occur along the pesticide's emission route appears to be an important screening parameter to assess environmental risks.

Adsorption and degradation of phenoxyalkanoic acid herbicides in soils: A review

“…The values of 1/n may differ for particular phenoxyalkanoic acid herbicides. The mean value of the parameter 1/n for 2,4-D, calculated for 37 soils from the A horizon, amounted to 0.91 (standard error [SE] ¼ 0.011) [43,[56][57][58], whereas it was 0.80 (SE ¼ 0.13) for MCPA in 23 soils from the same horizon [38,40,41,45,58,[60][61][62][63]. The few available studies on the shape of adsorption isotherms in soil profiles suggest that, for MCPA, the values of the parameter 1/n are the same for topsoils and subsoils [38,45], whereas the 1/n values are higher in the deeper soil horizons for 2,4-D [57].…”

“…It was indicated that in sterilized soils either no degradation of herbicides from this group was observed [87,94,95] or the degradation rate was much slower than in nonsterilized soils [96]. Moreover, soil degradation of phenoxyalkanoic acid herbicides was approximately 10 times slower at low oxygen concentrations [63], and under anaerobic conditions it was not observed [67,97]. The degradation rate of phenoxyalkanoic acid herbicides was positively correlated with the microbial biomass content as measured by the substrateinduced respiration [98][99][100] and the microbial activity estimated based on the dehydrogenase activity or fluorescein diacetate hydrolysis [99,100].…”

Alphaproteobacteria dominate active 2‐methyl‐4‐chlorophenoxyacetic acid herbicide degraders in agricultural soil and drilosphere

“…A high water content in 8-10 cm soil might have stimulated the formation of anoxic microzones (Zausig et al, 1993). Although anaerobic degradation via dechlorination of PAAs might occur under anoxic conditions, and anoxic microzones exist in soils depending on the water content, oxic degradation is considered to be the primary route of PAA degradation in soils (Haggblom, 1992;Zausig et al, 1993;Vink and vanderZee, 1997;Zipper et al, 1999). Thus, the data might suggest that Clostridiaceae/ 'Lachnospiraceae'-related taxa assimilated MCPA degradation products provided by aerobes, or fed on dead MCPA degraders (i.e.…”

“…The earthworm gut is rich in organic nutrients, is anoxic and sustains high microbial activities. However, rapid MCPA degradation requires molecular oxygen, indicating that the absence of oxygen in the earthworm gut precludes MCPA degradation (Vink and vanderZee, 1997;Zipper et al, 1999;Horn et al, 2003;Wüst et al, 2009). Indeed, MCPA degraders in the earthworm gut were not detected by most probable numbers , suggesting that conditions in the anoxic earthworm gut severely impair ingested MCPA degraders.…”

The earthworm Aporrectodea caliginosa stimulates abundance and activity of phenoxyalkanoic acid herbicide degraders

“…MCPA degradation requires molecular oxygen (Kuhlmann et al, 1995;Vink and vanderZee, 1997). Thus, increasing soil aeration by macropore formation might stimulate MCPA degradation and associated organisms.…”