Degradation and sorption of imidacloprid in dissimilar surface and subsurface soils

Degradation and sorption/desorption are important processes affecting the leaching of pesticides through soil. This research characterized the degradation and sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine) in Drummer (silty clay loam) and Exeter (sandy loam) surface soils and their corresponding subsurface soils using sequential extraction methods over 400 days. By the end of the incubation, approximately 55% of imidacloprid applied at a rate of 1.0 mg kg(-1) degraded in the Exeter sandy loam surface and subsurface soils, compared to 40% of applied imidacloprid within 300 days in Drummer surface and subsurface soils. At the 0.1 mg kg(-1) application rate, dissipation was slower for all four soils. Water-extractable imidacloprid in Exeter surface soil decreased from 98% of applied at day 1 to >70% of the imidacloprid remaining after 400 d, as compared to 55% in the Drummer surface soil at day 1 and 12% at day 400. These data suggest that imidacloprid was bioavailable to degrading soil microorganisms and sorption/desorption was not the limiting factor for biodegradation. In subsurface soils > 40% of (14)C-benzoic acid was mineralized over 21 days, demonstrating an active microbial community. In contrast, cumulative (14)CO(2) was less than 1.5% of applied (14)C-imidacloprid in all soils over 400 d. Qualitative differences in the microbial communities appear to limit the degradation of imidacloprid in the subsurface soils.     

Ultrasonic decomposition of atrazine and alachlor in water.

Abstract

The collapse of ultrasonically‐generated cavitation bubbles can result in sonochemical reactions. The kinetics of sonochemical decomposition of alachlor and atrazine in water were determined using a sonicator operating in the continuous mode at maximum output. Alachlor and atrazine solutions, 3.1 nmol L^‐1, were kept at constant temperature during the sonication. Decomposition at 30°C followed first‐order kinetics: k = 8.01 × 10^‐3 min^‐1 and 2.10 × 10^‐3 min^‐1 for alachlor and atrazine, respectively. It is not clear from the product analysis whether the decomposition was due to a thermal or free radical reaction. However, regardless of the decomposition mechanisms, the extrapolated half‐lives (86 and 330 min for alachlor and atrazine, respectively) support the potential development of ultrasonic waves to decompose herbicides in contaminated water.     

Biodegradation of imidacloprid by an isolated soil microorganism

Imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine), a chloronicotinyl insecticide used to control biting and sucking insects, is very persistent in the soil with a half-life often greater than 100 days. Although a few soil metabolites have been reported in the literature, there are no reports of imidacloprid-degrading soil microorganisms. Our objectives were to discover, isolate, and characterize microorganisms capable of degrading imidacloprid in soil. Two soil-free stable enrichment cultures in N-limited media were obtained that degraded 19 mg L(- 1) (43%) and 11 mg L(- 1) (16%) of the applied imidacloprid, and produced about 19 mg L(- 1) 6-chloronicotinic acid in three weeks. Enrichment media without microorganisms had no loss of imidacloprid. Strain PC-21, obtained from the enrichment cultures, degraded 37% to 58% of 25 mg L(- 1) imidacloprid in tryptic soy broth containing 1 g L(- 1) succinate and D-glucose at 27 degrees C incubation over a period of three weeks. Trace amounts of NO(3)(-)/NO(2)(-)were produced and six metabolites were characterized by high performance liquid chromatography (HPLC) using (14)C-methylene-imidacloprid and liquid chromatograph-electrospray-mass spectrometer (LC-MS). Two of the metabolites were identified as imidacloprid-guanidine and imidacloprid-urea by HPLC standards and LC-MS. During the experiment, 6-chloronicotinic acid was not produced. Less than 1% of the applied (14)C was incorporated into the microbial biomass and no (14)CO(2) was detected. Strain PC-21, identified as a species of Leifsonia by PCR amplification of a 500 bp sequence of 16s rRNA, cometabolized imidacloprid.     

Differences in herbicide adsorption on soil using several soil ph modification techniques

Abstract

Effects of soil pH on weak acid and weak base herbicide adsorption by soil are often determined by modifying soil pH in the laboratory. Modification of soil pH with acidic or basic amendments such as HCl or NaOH can cause changes in the soil‐solution system that may affect pesticide adsorption. The partition coefficients (K_d) for atrazine and dicamba by Waukegan, Piano, and Walla Walla silt loam soils stabilized in the field at different pH levels were compared to the K_d obtained when the soil pH was adjusted with acidic or basic amendments before herbicide addition. NaOH addition to raise soil pH generally increased the soluble soil organic carbon (SSOC) concentration in solution compared to field soils at the same pH and to soil treated with Ca(OH)₂. NaOH decreased the soil solution ionic strength slightly. Acidifying soils increased the soil solution ionic strength, when compared to field soils at the same pH and had no effect on SSOC concentration. Dicamba adsorption to soil was minimal (K_d < 0.22) and not influenced by soil pH in the range of 4.1 to 6.0; adsorption by laboratory amended soils in some cases underestimated adsorption compared to nonamended soils. Atrazine adsorption increased with decreased pH in all soils, and was overestimated slightly by several laboratory treatments to reduce pH compared to adsorption by field soils. Treatments to raise the pH did not affect atrazine adsorption. Overall, herbicide adsorption differences due to pH modification were small (<30%), and were not affected by soil solution ionic strength, saturating cation, or SSOC concentration in solution.     

Removal by sorption and in situ biodegradation of oil spills limits damage to marine biota: a laboratory simulation

This study examined the efficiency of cotton grass fibers in removing diesel oil from the surface of water in conditions prevailing in the Baltic Sea. The effect of low temperature, salinity, and bacterial amendments were tested in laboratory-scale set-ups, whereas 600-L mesocosms filled with Baltic Sea water were used for testing the effects of diesel oil and rapid removal of the oil on microorganisms, phytoplankton, and mussels. Cotton grass proved to be an excellent sorbent for diesel oil from the water surface at a low temperature. Inoculation with diesel-enriched microorganisms enhanced degradation of oil significantly in laboratory-scale experiments. In mesocosm experiments, the addition of diesel oil (0.66 mg L(-1), 0.533 L m(-2)) to the basins resulted in higher microbial density than in all other basins, including inoculated ones, suggesting that the Baltic Sea contains indigenous hydrocarbon degraders. The removal of oil with cotton grass significantly improved the survival of mussels in the mesocosm tests: 100% mortality in diesel basins versus 0% mortality in basins with cotton grass, respectively. However, the surviving mussels suffered from histopathological changes such as inflammatory responses, degenerations, and cell death. The observed rescuing effect was observable even when the cotton grass-bound oil was left in the water. The results underline the importance of rapid action in limiting damage caused by oil spills.     

Sorption and predicted mobility of herbicides in Baltic soils

This study was undertaken to determine sorption coefficients of eight herbicides (alachlor, amitrole, atrazine, simazine, dicamba, imazamox, imazethapyr, and pendimethalin) to seven agricultural soils from sites throughout Lithuania. The measured sorption coefficients were used to predict the susceptibility of these herbicides to leach to groundwater. Soil-water partitioning coefficients were measured in batch equilibrium studies using radiolabeled herbicides. In most soils, sorption followed the general trend pendimethalin > alachlor > atrazine～ amitrole～ simazine > imazethapyr > imazamox > dicamba, consistent with the trends in hydrophobicity (log K_ow) except in the case of amitrole. For several herbicides, sorption coefficients and calculated retardation factors were lowest (predicted to be most susceptible to leaching) in a soil of intermediate organic carbon content and sand content. Calculated herbicide retardation factors were high for soils with high organic carbon contents. Estimated leaching times under saturated conditions, assuming no herbicide degradation and no preferential water flow, were more strongly affected by soil textural effects on predicted water flow than by herbicide sorption effects. All herbicides were predicted to be slowest to leach in soils with high clay and low sand contents, and fastest to leach in soils with high sand content and low organic matter content. Herbicide management is important to the continued increase in agricultural production and profitability in the Baltic region, and these results will be useful in identifying critical areas requiring improved management practices to reduce water contamination by pesticides.