Pesticides are commonly applied around residential homes, but their occurrence on exterior surfaces (e.g., pavement) has not been thoroughly evaluated. We collected 360 dust samples from curbside gutters, sidewalks, and street surfaces at 40 houses in southern California to evaluate pesticide occurrence on urban paved surfaces as well as their spatial and temporal distributions. Pesticides and select degradates were ubiquitously detected in dust, with the median concentration of total target analytes at 85 μg kg-1. A total of 75% of samples contained at least five pesticides. As a result of recurring pesticide applications, concentrations increased throughout the summer. The pyrethroids bifenthrin and permethrin accounted for 55% of total pesticides detected in the dust. The highest concentrations in dust were found on the sidewalk and in the gutter. Relative to indoor environments, human exposure risk to pesticides on paved surfaces was estimated to be lower, with the highest potential oral and dermal exposure predicted to be 38 ng day-1 for permethrin. The ubiquitous detection of pesticides on residential outdoor surfaces and the fact that the exterior concentrations did not correlate to the indoor areas highlight the necessity to measure pesticides in both indoor and outdoor areas for complete residential pesticide risk assessment.

Strawberry harvesters hand-pick fruit that may result in pesticide exposure from hand foliar contact. This paper included a review of publications on harvester pesticide exposure, an observation of their work activities, and development of an alternative model for pesticide exposure prediction. Previous studies monitored the dermal pesticide exposure of strawberry harvesters and found most of the exposure (>70%) was on the hands. Exposure rates (ERs) were calculated as pesticide amount on the skin per hour worked, assuming foliar contact is proportional to daily work hours. Transfer factors (TFs), used for predicting exposure, were calculated by dividing the ER by the amount of dislodgeable foliar pesticide residue. However, the ERs for harvesters working in the same field at the same time varied by as much as 10-fold, and TFs calculated from different studies varied by up to 100-fold. We tested the assumption of foliar contact time being proportional to daily work hours. We observed full work-day activities of 32 strawberry harvesters. We found that their foliar contact time per work minute differed by up to 46%. We suggested using the amount of strawberries picked to predict harvester foliar contact. For all observed harvesters, their foliar contact time per kg of strawberries picked was 35±5 s. This value was similar among harvesters with varying years of experience, of different gender, and using gloves or not. We proposed a predictive model using the amount of strawberries picked to predict harvester pesticide exposure. The exposure predicted by the model is close to the exposure measured in previous monitoring studies ( R 2 : 0.84). The model slope is 0.33±0.03 × 10 3 cm 2 /kg. Model prediction accuracy was confirmed by monitoring captan exposure to harvesters in two fields. The model may be used as a quick screening method to estimate pesticide exposure before conducting complex human monitoring research.

Impervious pavements such as concrete are a dominant feature of urban landscapes, but their role in the fate of environmental contaminants is largely ignored. This study considered the case of urban-use pesticides, and demonstrated for the first time that surfaces such as concrete were capable of converting pesticides to other biologically active intermediates. Rapid transformation of pesticides was observed in both bench and field scale setups. Under outdoor conditions, permethrin, a heavily used pyrethroid insecticide, quickly formed 3-phenoxybenzoic acid (3-PBA) that is a known endocrine disruptor, and the level of 3-PBA was >100μg/L in the runoff water even 3months after the treatment. Fipronil, a product used for termite and ant control, was quickly transformed to desulfinyl and sulfone derivatives, with the desulfinyl level exceeding that of parent in the runoff water only 1week after treatment. Fipronil derivatives have aquatic toxicity similar or even greater than the parent fipronil. Direct sampling of deposited particles from residential exterior pavements revealed widespread presence of fipronil sulfone and desulfinyl and demonstrated their in-situ formation and accumulation on concrete. The extensive transformations were likely caused by the alkalinity and metal oxides in concrete and conducive photolytic conditions at the hard surfaces. The study findings highlight the role of urban pavements and urbanization in the geochemical cycling of anthropogenic contaminants.

BACKGROUNDPesticides are routinely applied to residential impervious outdoor surfaces for structural pest control. This residential usage has been linked to the occurrence of toxic levels of pesticides in urban water bodies. It is believed that run-off water transports particles that have sorbed hydrophobic pesticides. However, concentrations of particle-bound pesticides have not been directly measured on impervious surfaces, and the role of these particles as a source of contamination is unknown.RESULTSPesticides were detected in 99.4% of samples, with >75% of samples containing at least five pesticides. Assuming all particles were transferred with run-off, the run-off amount of pesticide during each rainfall would be >5 mg. We also used the US EPA Storm Water Management Model and estimated that 43 and 65% of the pesticides would be washed off during two rainfall events, with run-off concentrations ranging from 10.0 to 54.6 ng L(-1) and from 13.3 to 109.1 ng L(-1) respectively. The model-predicted pesticide run-off concentrations were similar to the levels monitored in urban run-off and sediments. Most (78%) particle samples contained aggregate toxicities above the Hyalella azteca LC50 .CONCLUSIONThe results suggest that loose particles on residential impervious surfaces are not only carriers but also an important source of hydrophobic pesticides in urban run-off and contribute to downstream aquatic toxicities. © 2015 Society of Chemical Industry.

Fipronil is a phenylpyrazole insecticide first registered in U.S. in 1996 and in California, is exclusively used for urban structural pest control and landscape maintenance. Although commonly found in urban waterways, runoff potential of fipronil from urban surfaces was seldom assessed, and with different physicochemical properties, conclusions obtained from pyrethroid runoff may not be applicable to fipronil. We conducted a field study by placing concrete blocks in real environment, treating the surfaces with fipronil, and analyzing surface runoff after simulated or natural precipitation. Isopropanol-wetted sponges were simultaneously used to wipe concrete surfaces for runoff prediction. The results showed during repeated precipitations fipronil residue could remain on the concrete for up to 3 months, and fipronil could still be detected in natural rainfall-induced runoff even 7 months after fipronil treatment. Compared to pyrethroids, fipronil has better water transferability. The wash-off in Day 1 was 2.1 +/- 0.7 % of applied amount, higher than 0.8 +/- 0.5 % for bifenthrin and 0.7 0.5 % for permethrin. However, fipronil is less persistent, and the runoff half-life was 17.2 d. Unlike pyrethroids, 81.1-96.7 % of runoff fipronil was dissolved in the aqueous phase, implying the potential for long-distance transport and better bioavailability. The surface wiping method successfully measured fipronil on concrete, and the same linear model developed for pyrethroids could be also used on fipronil, even for different precipitation schemes and after different periods of post-treatment exposure.

The pyrethroid insecticide bifenthrin is frequently detected at ng/L concentrations in tributaries of the San Francisco Bay Delta. The estuary is also experiencing increasing salinity through climate change and water redirection. To evaluate the impacts of hypersaline conditions on bifenthrin toxicity in anadromous salmonids of the San Francisco Bay Delta (CA, USA), a 14-d laboratory exposure was performed using 2 strains of Oncorhynchus mykiss (rainbow trout and steelhead) acclimated to freshwater and to 8g/L and 17g/L salinity. The fish were then exposed to nominal concentrations of 0 mu g/L, 0.1 mu g/L, and 1.5 mu g/L bifenthrin. Rainbow trout exhibited significant mortality following exposure to 1.5 mu g/L (1.07 +/- 0.35 mu g/L measured) bifenthrin in freshwater. Elevated levels of Na+/K+ adenosine triphosphatase 1A mRNA subunit expression was observed in the gill of rainbow trout acclimated to hypersaline conditions relative to freshwater animals. No significant difference was noted in Na+/K+ adenosine triphosphatase subunit levels in brains of either strain in freshwater or hypersaline conditions. Likewise, significant differences were not observed in plasma vitellogenin or steroid hormone concentrations in either strain whether maintained in freshwater or saltwater. Saltwater acclimation significantly reduced nicotinamide adenine dinucleotide phosphate-catalyzed biotransformation of bifenthrin in liver microsomes of rainbow trout but not of steelhead. The present study showed that, relative to steelhead, rainbow trout have different responses to bifenthrin acute toxicity as well as different rates of hepatic bifenthrin biotransformation and regulation of Na+/K+ adenosine triphosphatase subunits in gills. These data indicate that significant differences exist between the strains and that animal life history may have important effects on the susceptibility of each strain to environmental contaminants. Environ Toxicol Chem 2013;32:2779-2785. (c) 2013 SETAC

BACKGROUND Urban and residential concrete surfaces are often treated with pesticides to control ants. Run-off from irrigation/rainfall can remove pesticides from concrete and contaminate urban waterways. Recent regulations and mitigations in regions such as California aim to reduce insecticide run-off (e.g. pyrethroids), but are often proposed without adequate consideration of their impact on ant control efficacy. METHODS We carried out an outdoor study with a side-by-side comparison between pesticide run-off potential and residual ant toxicity after exposing treated concrete to summer conditions and simulated precipitations. RESULTS Treatments with bifenthrin, permethrin or fipronil all showed fast ant knockdown initially, and over 50% of ants were killed within 16 h after 1-min contact with the treated surfaces. Shorter ant median lethal time (LT50) was observed on concrete treated with over-the-counter (OTC) granule/dust formulations than OTC liquid or professional formulations. However, the treated surfaces rapidly lost ant control efficacy after outdoor exposure and repeated precipitations. Except for OTC solid permethrin treatment, the ant toxicity disappeared after 20 days for all other formulation treatments. In contrast, pesticides were detected in run-off water from simulated precipitations even 89 days after the treatment, with levels above 0.5 µg L(-1) for bifenthrin, 30 µg L(-1) for permethrin and 0.15 µg L(-1) for fipronil. Pyrethroid run-offs from OTC solid formulations were >10 times higher than the other two formulations. CONCLUSIONS The results suggested viable options for run-off mitigation include decreasing use on concrete such as using crack/spot treatments instead of broadcast applications, limiting pesticide use on hardscapes away from water contact, and avoiding using dust/granule formulations on hardscapes.

Pesticides such as pyrethroids have been frequently found in runoff water from urban areas and the offsite movement is a significant cause for aquatic toxicities in urban streams and estuaries. To better understand the origination of pesticide residues in urban runoff, we investigated the association of pyrethroid residues with loose particles in runoff water from concrete surfaces after treatment with commercial products of bifenthrin and permethrin. In runoff water generated from simulated precipitations after 1 to 89 d exposure under dry outdoor conditions, over 80% of the pesticides was found on particles >0.7 μm for most treatments. The solid-water partitioning coefficient (K(d)) on day 1 was estimated to be 2.4 × 10(3) to 1.1 × 10(5) L/kg for permethrin and bifenthrin on these solids. Except for solid formulations, the pesticide-laden particles likely originated from dust particles preexisting on the concrete before treatment and the disintegration of the surficial concrete matter through weathering. We consequently tested a simple sponge-wipe method to collect and analyze the loose particles on concrete. Concurrent analyses (n = 30) showed an excellent linear correlation between the amount of pesticides transferrable to runoff water and that on the wipe (R(2) = 0.78, slope = 1.13 ± 0.11, P < 0.0001). The fact that the linear relationship has a slope close to 1.0 suggests that this method may be used to predict pesticide residues available for contaminating runoff water before runoff actually occurs. The importance of loose particles should be considered when developing practices to mitigate pesticide runoff contamination from urban residential areas.

Intensive residential use of insecticides has resulted in their ubiquitous presence as contaminants in urban surface streams. For pest eradication, urban hard surfaces such as concrete are often directly treated with pesticides, and wind/water can also carry pesticides onto hard surfaces from surrounding areas. This study expanded on previous bench-scale studies by considering pesticide runoff caused by irrigation under dry weather conditions and rain during the wet season, and evaluated the effects of pesticide residence time on concrete, single versus recurring precipitations, precipitation intensity, and concrete surface conditions, on pesticide transferability to runoff water. Runoff from concrete 1 d after pesticide treatment contained high levels of bifenthrin (82 μg/L) and permethrin (5143 μg/L for cis and 5518 μg/L for trans), indicating the importance of preventing water contact on concrete after pesticide treatments. Although the runoff transferability quickly decreased as the pesticide residence time on concrete increased, detectable residues were still found in runoff water after 3 months (89 d) exposure to hot and dry summer conditions. ANOVA analysis showed that precipitation intensities and concrete surface conditions (i.e., acid wash, silicone seal, stamping, and addition of microsilica) did not significantly affect the pesticide transferability to runoff. For concrete slabs subjected to natural rainfalls during the winter wet season, pesticide levels in the runoff decreased as the time interval between pesticide application and the rain event increased. However, bifenthrin and permethrin were still detected at 0.15-0.17 and 0.75-1.15 μg/L in the rain runoff after 7 months (221 d) from the initial treatment. In addition, pesticide concentrations showed no decrease between the two rainfall events, suggesting that concrete surfaces contaminated by pesticides may act as a reservoir for pesticide residues, leading to sustained urban runoff contamination.