Svetlana Bondarenko

Persistence of selected organophosphate and carbamate insecticides in waters from a coastal watershed.

Organophosphate and carbamate compounds are among the most widely used pesticides. Contamination of surface water by these compounds is of concern because of potential toxicity to aquatic organisms, especially those at lower trophic levels. In this study we evaluated the persistence of diazinon, chlorpyrifos, malathion, and carbaryl in waters from various sites in the Newport Bay-San Diego Creek watershed in southern California (USA). The persistence of diazinon and chlorpyrifos was much longer than that of malathion or carbaryl and was further prolonged in seawater. Microbial degradation contributed significantly to the dissipation of diazinon and chlorpyrifos in freshwater, but was inhibited in seawater, leading to increased persistence. In contrast, degradation of malathion and carbaryl was rapid and primarily abiotic. A greater temperature dependence was observed for carbaryl degradation in all waters and for diazinon degradation in freshwater. The interactions of pesticide persistence with water location, temperature, and type of pesticides suggest that site- and compound-specific information is needed when evaluating the overall ecotoxicological risks of pesticide pollution in a watershed. Because the persistence of diazinon and chlorpyrifos may increase significantly in seawater, mitigation should occur before the pesticides reach seawater. The relatively short persistence of these compounds in freshwater suggests that practices aimed at extending residence time (e.g., diversion to wetlands) may effectively reduce pesticide output to downstream water bodies.

Occurrence of fipronil and its biologically active derivatives in urban residential runoff.

Insecticides are commonly used around homes for controlling insects such as ants, termites, and spiders. Such uses have been linked to pesticide contamination and toxicity in urban aquatic ecosystems. Fipronil is a relatively new and popular urban-use insecticide that has acute toxicity to arthropods at low-ppb levels. In this study, we collected runoff water from 6 large communities, each consisting of 152 to 460 single-family homes, in Sacramento County and Orange County, California, and evaluated the occurrence of fipronil and its biologically active derivatives over 26 months under dry weather conditions. Statistical modeling showed that the levels of fipronil and derivatives in the runoff water were both spatially and temporally correlated. More than 10-fold differences were observed between the Sacramento and Orange County sites, with the much higher levels for Orange County (southern California) coinciding with heavier use. The median concentrations of combined fipronil and derivatives for the Orange County sites were 204-440 ng L(-1), with the 90th percentile levels ranging from 340 to 1170 ng L(-1). These levels frequently exceeded the LC50 values for arthropods such as mysid shrimp and grass shrimp. The highest levels occurred from April to October, while decreases were seen from October to December and from January to March, likely reflecting seasonal use patterns and the effect of rain-induced washoff. Fipronil and fipronil sulfone (oxidation derivative) each accounted for about 35% of the total concentrations, with desulfinyl fipronil (a photolytic product) contributing about 25%. Results of this study clearly established residential drainage as a direct source for pesticide contamination in urban waterways, and for the first time, identified fipronil as a new and widespread contaminant with potential ecotoxicological significance.

Degradation and sorption of selected organophosphate and carbamate insecticides in urban stream sediments

Monitoring studies show that urban surface streams in the United States are commonly contaminated with pesticides, and contamination by organophosphates and carbamates is of particular concern because of their aquatic toxicity. The degradation and sorption of four common organophosphate and carbamate insecticides were studied in urban creek sediments from southern California, USA. In sediment, malathion was quickly degraded under either aerobic or anaerobic conditions, with a half-life (t(1/2)) <3 d. Diazinon and chlorpyrifos were moderately persistent under aerobic conditions (t(1/2) = 14-24 d). However, persistence of chlorpyrifos increased significantly under anaerobic conditions, and t(1/2) was prolonged to 58 to 223 d. The greatest effect of redox potential was found with carbaryl. Although rapid dissipation occurred under aerobic conditions (t(1/2) = 1.8-4.9 d), carbaryl became virtually nondegradable under anaerobic conditions (t(1/2) = 125-746 d). The sorption coefficient consistently increased with time for all pesticides, and chlorpyrifos displayed greater sorption potential than the other pesticides. This study indicates that pesticides in sediment may become less available with time because of increased sorption, and pesticide persistence in sediment may vary greatly among compounds and with redox conditions. Under anaerobic conditions, long persistence may occur even for nonpersistent compounds.

Analysis of pyrethroids in sediment pore water by solid-phase microextraction

Sediment toxicity from trace contamination of pyrethroid insecticides is an emerging water quality concern. Pyrethroids are highly hydrophobic, and their sediment toxicity is related to the freely dissolved concentration in pore water. Solid-phase microextraction (SPME) was evaluated as a selective method to analyze free concentrations of eight pyrethroids in sediment pore water, and SPME measurements were compared to total pore-water concentrations measured using a conventional liquid-liquid extraction (LLE) method. Free pore-water concentrations detected by SPME (C(w-SPME)) were 4.1 to 37% of the total concentration given by LLE (C(w-LLE)) in pore water prepared from a freshwater sediment and only 3.2 to 13.3% in the pore water of a marine sediment. The difference suggested predominant partitioning of pyrethroids into the dissolved organic matter phase in pore water. The method detection limits of the SPME method were lower than the 10th percentile of the reported median lethal concentrations for aquatic organisms, with relative standard deviation <20% as determined over 200 analyses. The SPME method was further used to analyze field-contaminated sediment samples. Those analyses showed that the phase distribution of pyrethroids in sediment was influenced by sediment type and other conditions. Our results show that SPME provides a sensitive, reproducible, and practical method for screening sediment toxicity from potential pyrethroid contamination.

Removal mechanisms and fate of insecticides in constructed wetlands

Constructed wetlands (CWs), along with other vegetative systems, are increasingly being promoted as a mitigation practice to treat non-point source runoff to reduce contaminants such as pesticides. However, studies so far have mostly focused on demonstrating contaminant removal efficiency. In this study, using two operational CWs located in the Central Valley of California, we explored the mechanisms underlying the removal of pyrethroids and chlorpyrifos from agricultural runoff water, and further evaluated the likelihood for the retained pesticides to accumulate within the CWs over time. In the runoff water passing through the CWs, pyrethroids were associated overwhelmingly with suspended solids >0.7 μm, and the sorbed fraction accounted for 38-100% of the total concentrations. The derived K(d) values for the suspended solids were in the order of 10(4)-10(5), substantially greater than those reported for bulk soils and sediments. Distribution of pyrethroids in the wetland sediments was found to mimic organic carbon distribution, and was enriched in large particles that were partially decomposed plant materials, and clay-size particles (<2 μm). Retention of suspended particles, especially the very large particles (>250 μm) and the very fine particles, is thus essential in removing pyrethroids and chlorpyrifos in CWs. Under flooded and anaerobic conditions, most pyrethroids and chlorpyrifos showed moderate persistence, with DT(50) values between 106-353 d. However, the retained pyrethroids were very stable in dry and aerobic sediments between irrigation seasons, suggesting a possibility for accumulation over time. Therefore, the long-term ecological risks of CWs should be further understood before their wide adoption.

Enantioselectivity in fipronil aquatic toxicity and degradation

Fipronil and its transformation products are being increasingly detected in aquatic ecosystems as a result of widespread use. Fipronil is a chiral compound, and enantioselectivity may greatly impact its environmental fate and effects. In the present study, fipronil enantiomers were isolated and used to investigate the possibility of enantioselectivity in their acute toxicity to Japanese medaka (Oryzias latipes) and cytotoxicity to primary hepatocytes from rainbow trout (Oncorhynchus mykiss). Enantioselectivity was further evaluated in terms of fipronil degradation in sediments under aerobic and anaerobic conditions and in field-contaminated runoff water from urban watersheds. The 96-h median lethal concentrations to Japanese medaka were 94.2 (95% confidence interval [CI], 82.9-107.1), 98.3 (95% CI, 85.6-113.0), and 95.4 (95% CI, 74.7-121.9) microg/L for the racemic, R-(-)-, and S-(+)-fipronil, respectively, suggesting absence of enantioselectivity. The 24-h median effect concentration of racemic fipronil to primary rainbow trout hepatocytes was 26.7 (95% CI, 25.6-27.9) microg/ml. In contrast, exposure of the cells to the S-(+)- and R-(-)-enantiomers resulted in a 19.7 and 7.8% reduction in cell viability, respectively, at the highest treatment concentrations (100 microg/ml), potentially indicating a greater-than-additive interaction between enantiomers. Under aerobic or slightly reduced conditions, biodegradation of fipronil in sediments was essentially nonstereoselective, with the enantiomeric fraction (EF) similar to racemic (EF = 0.5) after 168 d of incubation. However, EF decreased to as low as less than 0.1 following short incubations under anaerobic conditions, suggesting preferential degradation of S-(+)-fipronil in strongly reduced sediments. A survey of urban runoff samples consistently showed near-racemic EF, indicating fipronil degradation that was not enantioselective. Results suggest that site-specific characteristics are critical in accurately predicting fipronil fate and toxicity in the environment.

Time dependence of phase distribution of pyrethroid insecticides in sediment

Synthetic pyrethroids are strongly hydrophobic compounds, and their toxicity in sediment is regulated by phase distribution among the sediment, dissolved organic matter, and water phases. In the present study, we spiked and equilibrated four pyrethroids in two sediments, and we characterized their phase distribution as a function of contact time. The freely dissolved concentration measured by solid-phase microextraction was only a small fraction (<16.3%) of the total pore-water concentration as determined by liquid-liquid extraction. The fraction of the freely dissolved concentration was significantly greater in the freshwater sediment (1.7-16.3%) than in the marine sediment (1.1-4.2%) following 9 d of equilibration, and it decreased substantially with contact time to less than 5% at 30 d after sediment dosing. Consequently, the apparent organic carbon partition coefficient (Koc) and dissolved organic carbon partition coefficient (Kdoc) values increased significantly over the contact time, especially in the freshwater sediment, suggesting that phase distribution was not at equilibrium after 9 d of equilibration. If only the freely dissolved concentration is bioavailable, these observations suggest that contact time after sediment dosing may greatly affect the bioavailability and, hence, the toxicity of pyrethroids. Therefore, a long contact time (> or = 30 d) is recommended for sediment toxicity testing of this class of compounds. The dependence of bioavailability on contact time also implies that test conditions must be standardized to allow comparison between laboratory-dosed samples and field samples.

Impact of ant control technologies on insecticide runoff and efficacy

BACKGROUND Insecticides are commonly used for ant control around residential homes, but post-treatment runoff may contribute to contamination of surface water in urban watersheds. This study represents the first instance where runoff of insecticides was directly measured after applications around single family residences. During 2007, houses were treated with bifenthrin or fipronil sprays following standard practices. During 2008, pin stream applicators, spray-free zones and restricting sprays to the house foundation were considered as management options. RESULTS During 2007, the resulting runoff from the bifenthrin spray in the irrigation water had a mean concentration of 14.9 microg L(-1) at 1 week post-treatment and 2.5 microg L(-1) at 8 weeks, both high enough to be toxic to sensitive aquatic organisms. In comparison, treatments with bifenthrin granules resulted in no detectable concentrations in the runoff water after 8 weeks. The mean concentration for fipronil used as a perimeter spray was 4.2 microg L(-1) at 1 week post-treatment and 0.01 microg L(-1) at 8 weeks, with the first value also suggesting a potential for causing acute aquatic toxicity to sensitive organisms. During 2008, insecticide runoff was reduced by using spray-free zones and pin stream perimeter applications. CONCLUSIONS It is shown that insecticide runoff from individual home treatments for ants can be measured and used to improve techniques that minimize runoff. The pin stream application and applications limited to the house foundation should be further evaluated for their potential to reduce pesticide runoff from residential homes.

Clothianidin in agricultural soils and uptake into corn pollen and canola nectar after multiyear seed treatment applications

Abstract Limited data are available on the fate of clothianidin under realistic agricultural production conditions. The present study is the first large‐scale assessment of clothianidin residues in soil and bee‐relevant matrices from corn and canola fields after multiple years of seed‐treatment use. The average soil concentration from 50 Midwest US corn fields with 2 yr to 11 yr of planting clothianidin‐treated seeds was 7.0 ng/g, similar to predicted concentrations from a single planting of Poncho 250‐treated corn seeds (6.3 ng/g). The water‐extractable (i.e., plant‐bioavailable) clothianidin residues in soil were only 10% of total residues. Clothianidin concentrations in soil reached a plateau concentration (amount applied equals amount dissipated) in fields with 4 or more application years. Concentrations in corn pollen from these fields were low (mean: 1.8 ng/g) with no correlation to total years of use or soil concentrations. For canola, soil concentrations from 27 Canadian fields with 2 yr to 4 yr of seed treatment use (mean = 5.7 ng/g) were not correlated with use history, and plant bioavailability was 6% of clothianidin soil residues. Average canola nectar concentrations were 0.6 ng/g and not correlated to use history or soil concentrations. Under typical cropping practices, therefore, clothianidin residues are not accumulating significantly in soil, plant bioavailability of residues in soil is limited, and exposure to pollinators will not increase over time in fields receiving multiple applications of clothianidin. Environ Toxicol Chem 2016;35:311–321.

Leaching of pharmaceuticals and personal care products in turfgrass soils during recycled water irrigation.

An important beneficial reuse of treated wastewater (recycled water) in arid and semiarid regions is landscape irrigation. However, the environmental fate, especially groundwater contamination potential, of trace contaminants such as pharmaceuticals and personal care products (PPCPs) is a significant concern that can hinder the acceptance and adoption of such reuses. In this study, we irrigated mature turfgrass plots with nonspiked tertiary treated wastewater for over 6 mo at 100 or 130% of the reference evapotranspiration rate (ETo) and collected leachate water at the 90-cm depth on a weekly basis. In the recycled water, all 14 target PPCPs were consistently found, and the mean levels of atenolol, gemfibrozil, meprobamate, carbamazepine, and sulfamethoxazole were above 100 ng L. However, only five compounds were detected in the leachate at trace levels. Trimethoprim and primidone were frequently found, whereas the detection of sulfamethoxazole, meprobamate and carbamazepine was less frequent (<50%). When detected, the overall mean concentration in the leachate was 10.2 ng L for trimethoprim, 7.1 ng L for primidone, and 2.9 to 12.4 ng L for carbamazepine, sulfamethoxazole, and meprobamate. The majority of the target PPCPs were completely removed. Given that the irrigation rates were higher than normal, this study clearly demonstrated the efficacy of turfgrass systems in attenuating PPCPs during recycled water irrigation. However, it is also apparent that some PPCPs are more susceptible to leaching than others, and these PPCPs thus merit further research attention.