Shifts in Biodegradation Kinetics of the Herbicides MCPP and 2,4-D at Low Concentrations in Aerobic Aquifer Materials

Abstract

Biodegradation kinetics of two phenoxy acid herbicides, MCPP [(+/-)-2-(4-chloro-2-methylphenoxy)propanoic acid; mecoprop] and 2,4-D [2,4-dichlorophenoxyacetic acid] were studied in laboratory batch microcosms at low concentrations (0.025-100 microg/L) using 14C technique with sediments and groundwater from a shallow aerobic sandy aquifer. Below a certain threshold concentration of approximately 1 microg/L for 2,4-D and 10 microg/L for MCPP, the biodegradation followed first-order nongrowth kinetics, and no adaptation was observed within the experimental period of 341 d. Half-lifes for ultimate degradation were 500 d for 2,4-D and 1100 d for MCPP at 10 degrees C in unpolluted aquifer sediment in this environmentally relevant concentration regime. Above the threshold concentrations, the biodegradation rate accelerated gradually due to selective growth of specific biomass, which was ascertained from 14C most probable number enumerations of specific phenoxy acid degraders. Atthe highest concentration tested (100 microg/ L), specific degraders increased from 10(-1) to 10(5) cells/g during the experiment, and half-lifes after adaptation decreased to approximately 5 d. The enhanced rate of degradation by adapted systems was maintained during degradation of the last residuals measured to less than 0.1 microg/L. In situ long-term preexposure of the aquifer sediment also resulted in significant higher degradation rates of the phenoxy acids.

Mecoprop (MCPP) removal in full-scale rapid sand filters at a groundwater-based waterworks

“…This corresponds to previous observations of aerobic biodegradation of MCPP with aquifer materials (Janniche et al, 2010;Toräng and Albrechtsen, 2003). However, an adaptation phase of more than 16 days is required before MCPP degradation is initiated in aquifer material (Agertved et al, 1992;Tuxen et al, 2000;Janniche et al, 2010).…”

Freshwater sediment pesticide biodegradation potential as an ecological indicator of microbial recovery following a decrease in chronic pesticide exposure: A case study with the herbicide diuron

“…In summer 2007, a similar gradual increase in diuron mineralization potential along the Morcille river was reported, with higher diuron-mineralizing ability observed in the downstream section of the river for both periphytic biofilm and sediment communities (Pesce et al, 2009). It is noteworthy that studies on the potential of natural freshwater sediments to degrade synthetic pesticides are scarce ( Kalsch et al, 1998, Larsen et al, 2000, Toräng et al, 2003and Trinh et al, 2012, but there is now convincing evidence that the capacity of microbial sediment communities to biodegrade these contaminants can increase after an in situ longterm pre-exposure to these compounds ( Toräng et al, 2003 andTrinh et al, 2012). In the present study, the estimation of diuron-mineralizing ability in the sediments of the Morcille river differentiated the reference (upstream) from the two (intermediate and downstream) exposed stations.…”

“…It has been shown that the development of pesticide biodegradation capacities in natural microbial communities, in both soils (e.g. Sørensen et al, 2003, Dellamatrice and Monteiro, 2004and El-Sebai et al, 2005; for phenylurea herbicides) and sediments (Toräng et al, 2003, Pesce et al, 2010band Trinh et al, 2012 occurs in response to repeated exposure to pesticide. The stable, low mineralization potential observed upstream thus clearly reflected the steady low level of diuron exposure recorded in this river section during the four-year survey period.…”

Kinetics and Yields of Pesticide Biodegradation at Low Substrate Concentrations and under Conditions Restricting Assimilable Organic Carbon

“…Comparatively few studies have investigated microbial growth and yield of bacterial strains at low substrate concentrations (12,13). Several authors have reported threshold concentrations (typically less than 10 g liter Ϫ1 ) below which degradation continues in a nongrowth regime (9,11,14), but these conclusions are based solely on observed first-order substrate utilization kinetics; direct measurements of microbial growth or yield at these low concentrations have not been reported.…”