Donald P. Weston

Use and toxicity of pyrethroid pesticides in the Central Valley, California, USA

The use of pyrethroid insecticides is increasing for agriculture, commercial pest control, and residential consumer use. In addition, there is a trend toward the use of newer and more potent compounds. Little is known about the toxicity of sediment-associated pyrethroid residues to aquatic organisms, yet recent work has shown they commonly are found in aquatic sediments in the heavily agricultural Central Valley of California, USA. Minimal data exist on the sensitivity of standard sediment toxicity testing species to pyrethroids, despite two or more decades of agricultural use of these compounds. Sediment concentrations causing acute toxicity and growth impairment to the amphipod Hyalella azteca were determined for six pyrethroids in three sediments, ranging from 1.1 to 6.5% organic carbon (OC). In order of decreasing toxicity of sediment-associated residues, the compounds tested were bifenthrin (average 10-d median lethal concentration [LC50] = 0.18 microg/g OC), lambda-cyhalothrin (0.45 microg/g OC), deltamethrin (0.79 microg/g OC), esfenvalerate (0.89 microg/g OC), cyfluthrin (1.08 microg/g OC), and permethrin (4.87 microg/g OC). In a sediment containing about 1% OC, most pyrethroids, except permethrin, would be acutely toxic to H. azteca at concentrations of 2 to 10 ng/g dry weight, a concentration only slightly above current analytical detection limits. Growth typically was inhibited at concentrations below the LC50; animal biomass on average was 38% below controls when exposed to pyrethroid concentrations roughly one-third to one-half the LC50. Survival data are consistent with current theory that exposure occurs primarily via the interstitial water rather than the particulate phase. A reanalysis of previously reported field data using these toxicity data confirms that the compounds are exceeding concentrations acutely toxic to sensitive species in many agriculture-dominated water bodies.

Antibacterial residues in marine sediments and invertebrates following chemotherapy in aquaculture

Abstract Salmon net-cage culturists in the USA use oxytetracycline, and to a lesser extent Romet ® 30 and amoxycillin, to prevent or treat bacterial disease. This study examined the environmental fate of oxytetracycline and Romet ® 30 at three farm sites and in flow-through, sediment microcosms dosed with antibacterials at rates intended to mimic farm conditions. The frequency of detection of oxytetracycline in sediments beneath the farms paralleled drug usage, with residues rarely detected beneath a farm that used very little oxytetracycline (8.5 kg active ingredient), and concentrations commonly between 0.5 and 4 μg g −1 at a farm that used 186 kg in a single prophylactic treatment period. The presence of oxytetracycline residues in surficial and subsurface sediments even before that treatment indicated persistence since at least the prior summer (10 months previous) or possibly longer. The area of sediments containing measurable oxytetracycline residues was very localized, however, with residues detectable only under the cages and to a distance of 30 m, but absent from a 100 m site. In laboratory microcosms, one-fourth to one-half of the oxytetracycline remained in microcosm sediments after 60 days, and the one treatment in which loss of the drug approximated an exponential curve indicated a 36-day half-life. Sulfadimethoxine and ormetoprim, the active ingredients in Romet ® 30, appeared to be very short-lived in marine sediments, based on preliminary data. Residues of both drugs at concentrations slightly above the analytical level of detection were found in one microcosm 2 days after the cessation of treatment, but no residues were found in microcosms 22–34 days after treatment or 21–62 days after treatment at two farm sites. We also collected crabs and oysters from the area surrounding the one farm that relied upon antibacterials most heavily. No more than trace oxytetracycline residues (about 0.1 μg g −1 ) were found in oysters ( Crassostrea gigas ) or Dungeness crab ( Cancer magister ) collected under the farm, but about half the red rock crab ( Cancer productus ) collected under the cages during and within 12 days of oxytetracycline treatment contained oxytetracycline in meat at concentrations of 0.8 to at least 3.8 μg g −1 , well in excess of the US Food and Drug Administration limit for commercially sold seafood of 0.1 μg g −1 .

Residential runoff as a source of pyrethroid pesticides to urban creeks

Pyrethroid pesticides occur in urban creek sediments at concentrations acutely toxic to sensitive aquatic life. To better understand the source of these residues, runoff from residential neighborhoods around Sacramento, California was monitored over the course of a year. Pyrethroids were present in every sample. Bifenthrin, found at up to 73 ng/L in the water and 1211 ng/g on suspended sediment, was the pyrethroid of greatest toxicological concern, with cypermethrin and cyfluthrin of secondary concern. The bifenthrin could have originated either from use by consumers or professional pest controllers, though the seasonal pattern of discharge from the drain was more consistent with professional use as the dominant source. Stormwater runoff was more important than dry season irrigation runoff in transporting pyrethroids to urban creeks. A single intense storm was capable of discharging as much bifenthrin to an urban creek in 3h as that discharged over 6 months of irrigation runoff.

Urban and Agricultural Sources of Pyrethroid Insecticides to the Sacramento-San Joaquin Delta of California

While studies have documented the presence of pyrethroid insecticides at acutely toxic concentrations in sediments, little quantitative data on sources exist. Urban runoff, municipal wastewater treatment plants and agricultural drains in Californias Sacramento-San Joaquin River Delta were sampled to understand their importance as contributors of these pesticides to surface waters. Nearly all residential runoff samples were toxic to the amphipod, Hyalella azteca, and contained pyrethroids at concentrations exceeding acutely toxic thresholds, in many cases by 10-fold. Toxicity identification evaluation data were consistent with pyrethroids, particularly bifenthrin and cyfluthrin, as the cause of toxicity. Pyrethroids passed through secondary treatment systems at municipal wastewater treatment facilities and were commonly found in the final effluent, usually near H. azteca 96-h EC(50) thresholds. Agricultural discharges in the study area only occasionally contained pyrethroids and were also occasional sources of toxicity related to the organophosphate insecticide chlorpyrifos. Discharge of the pyrethroid bifenthrin via urban stormwater runoff was sufficient to cause water column toxicity in two urban creeks, over at least a 30 km reach of the American River, and at one site in the San Joaquin River, though not in the Sacramento River.

Antibacterial resistant bacteria in surficial sediments near salmon net-cage farms in Puget Sound, Washington

Abstract Antibacterials are used in medicated fish feed at fish farms located in Puget Sound, Washington. These compounds include oxytetracycline (OTC), amoxycillin, and Romet ® 30 (a drug composed of sulfadimethioxine and ormetoprim). In this study we collected surficial sediment samples at three different commercial salmon net-cage farms during the summer and early fall of 1992. The three different farms varied in their use of antibacterials. Before beginning our field investigation we developed a modification of Mueller Hinton Agar to enumerate antibacterial-resistant bacteria. A synthetic seawater was added at 70% concentration to Mueller Hinton Agar. Because the divalent cations present in seawater chelate OTC, the concentration of this antibacterial was increased in the seawater medium relative to concentrations typically used in clinical microbiology laboratories. We enumerated the total number of cultivable bacteria, and bacteria resistant to oxytetracycline, amoxycillin, or Romet ® 30 by plating aliquots of sediment samples onto the marine Mueller Hinton Agar. The highest numbers of bacteria (10 6 to 10 8 colony forming units g −1 ) were generally found nearest the net-cages with densities declining about an order-of-magnitude further away from the cages. Farm A, which used the greatest amount of antibacterials of the three farms, had the highest percentages of antibacterial-resistant bacteria in the sediments. At this Farm resistance to Romet ® 30 and OTC tended to parallel each other, suggesting either a common resistance mechanism or linkage of the genes responsible for the resistances. Farm C used the least amount of antibacterials and this was reflected in that this farm also had the lowest percentage of sedimentary bacteria that were resistant to the antibacterials. Although the total number of bacteria at Farm C was in a similar range as found at Farms A and B, the percentages of antibacterial resistant bacteria were 5% or less for most of the samples. Our results suggest that a background of less than 5% of the cultivable bacteria in marine sediments is resistant to OTC, Romet ® 30, or amoxycillin.

Method development for the analysis of organophosphate and pyrethroid insecticides at low parts per trillion levels in water.

In the current study, organophosphate and pyrethroid insecticides including diazinon, chlorpyrifos, bifenthrin, fenpropathrin, permethrin, lambda-cyhalothrin, cyfluthrin, cypermethrin, esfenvalerate and deltamethrin were analyzed in laboratory and field-collected water samples. Water samples were extracted and analyzed by gas chromatography/electron capture detector (GC/ECD) and gas chromatography/nitrogen-phosphorous detector (GC/NPD). Comparison of results from liquid-liquid extraction and subsequent normal phase solid-phase extraction cleanup (LLE-NPSPE), and reversed phase solid-phase extraction (RPSPE) showed that LLE-NPSPE was the better choice to extract trace amounts of pesticides from water. Pesticide recoveries from four spiked water samples using LLE-NPSPE ranged from 63.2 to 148.8% at four spiking concentrations. Method detection limits were 0.72-1.69 ng/L using four different water sources. The stability of the target pesticides in lake water was investigated at 4 degrees C for 1h, 1d, 4d, and 7d under three conditions: (1) water samples only; (2) with 20 mL hexane used as a keeper solvent; and (3) with acidification to pH 2 with HCl. Results showed that water storage without treatment resulted in slow degradation of some pesticides with storage time, storage using water acidification led to significant degradation and loss of diazinon and chlorpyrifos, while water storage with hexane as a keeper solvent showed good stability for all of the target pesticides over the 7d storage period.

Whole sediment toxicity identification evaluation tools for pyrethroid insecticides: III. Temperature manipulation

Since the toxicity of pyrethroid insecticides is known to increase at low temperatures, the use of temperature manipulation was explored as a whole-sediment toxicity identification evaluation (TIE) tool to help identify sediment samples in which pyrethroid insecticides are responsible for observed toxicity. The amphipod Hyalella azteca is commonly used for toxicity testing of sediments at a 23 degrees C test temperature. However, a temperature reduction to 18 degrees C doubled the toxicity of pyrethroids, and a further reduction to 13 degrees C tripled their toxicity. A similar response, though less dramatic, was found for 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), and dissimilar temperature responses were seen for cadmium and the insecticide chlorpyrifos. Tests with field-collected sediments containing pyrethroids and/or chlorpyrifos showed the expected thermal dependency in nearly all instances. The inverse relationship between temperature and toxicity provides a simple approach to help establish when pyrethroids are the principal toxicant in a sediment sample that could be used as a supplemental tool in concert with chemical analysis or other TIE manipulations. The phenomenon appears to be, in part, a consequence of a reduced ability to biotransform the toxic parent compound at cooler temperatures. The strong dependence of pyrethroid toxicity on temperature has important ramifications for predicting their environmental effects, and the standard test temperature of 23 degrees C dramatically underestimates risk to resident fauna during the cooler months.

Multiple origins of pyrethroid insecticide resistance across the species complex of a nontarget aquatic crustacean, Hyalella azteca

Significance The crustacean, Hyalella azteca, is commonly used in environmental monitoring to test the toxicity of water or sediment. We show that among three laboratory cultures and seven wild populations of H. azteca, there is a more than 550-fold variation in sensitivity to widely used pyrethroid insecticides. Some individuals have attained resistance by mutations in the voltage-gated sodium channel, the target site for pyrethroid toxicity. Similar mutations have been found in agricultural pests targeted by pyrethroids, but this study indicates that runoff of terrestially applied urban and agricultural pesticides has been sufficient to induce resistance in a nontarget aquatic species on multiple, independent occasions. Our results have far-reaching implications for biomonitoring programs in general and especially those relying on H. azteca. Use of pesticides can have substantial nonlethal impacts on nontarget species, including driving evolutionary change, often with unknown consequences for species, ecosystems, and society. Hyalella azteca, a species complex of North American freshwater amphipods, is widely used for toxicity testing of water and sediment and has frequently shown toxicity due to pyrethroid pesticides. We demonstrate that 10 populations, 3 from laboratory cultures and 7 from California water bodies, differed by at least 550-fold in sensitivity to pyrethroids. The populations sorted into four phylogenetic groups consistent with species-level divergence. By sequencing the primary pyrethroid target site, the voltage-gated sodium channel, we show that point mutations and their spread in natural populations were responsible for differences in pyrethroid sensitivity. At least one population had both mutant and WT alleles, suggesting ongoing evolution of resistance. Although nonresistant H. azteca were susceptible to the typical neurotoxic effects of pyrethroids, gene expression analysis suggests the mode of action in resistant H. azteca was not neurotoxicity but was oxidative stress sustained only at considerably higher pyrethroid concentrations. The finding that a nontarget aquatic species has acquired resistance to pesticides used only on terrestrial pests is troubling evidence of the impact of chronic pesticide transport from land-based applications into aquatic systems. Our findings have far-reaching implications for continued uncritical use of H. azteca as a principal species for monitoring and environmental policy decisions.

Chemical availability and sediment toxicity of pyrethroid insecticides to Hyalella azteca: application to field sediment with unexpectedly low toxicity.

Tenax extraction is a simple, inexpensive approach to estimate the bioavailability of hydrophobic organic contaminants from sediment. In the present study, a single-point Tenax extraction was evaluated regarding its correlation with the acute toxicity to Hyalella azteca using field-collected sediments in California, USA. Pyrethroids were believed to be the primary contributor to the observed toxicity, and a significant correlation existed between the expected toxicity (given pyrethroid concentrations) and the mortality at most sampling sites. A small subset of sites, however, showed unexpectedly low toxicity to H. azteca despite high concentrations of pyrethroids. These samples were evaluated by Tenax extraction with the expectation that this procedure, which qualifies bioavailable instead of total pyrethroid concentration in sediment, would better explain the anomalously low toxicity. The term bioavailable toxic unit was proposed to link sediment toxicity with chemical availability, and the toxicity in the 17 selected sediments was better explained using Tenax extraction. The r2 value of the regression between sediment toxicity and toxic unit for the 17 sediments increased from 0.24 to 0.60 when the Tenax-extractable concentration was used in place of the total concentration. Results also showed that adsorption to sand particles might play a controlling role in pyrethroid bioavailability and, in turn, sediment toxicity to benthic invertebrates.

Pyrethroid insecticides in urban salmon streams of the Pacific Northwest

Urban streams of the Pacific Northwest provide spawning and rearing habitat for a variety of salmon species, and food availability for developing salmon could be adversely affected by pesticide residues in these waterbodies. Sediments from Oregon and Washington streams were sampled to determine if current-use pyrethroid insecticides from residential neighborhoods were reaching aquatic habitats, and if they were at concentrations acutely toxic to sensitive invertebrates. Approximately one-third of the 35 sediment samples contained measurable pyrethroids. Bifenthrin was the pyrethroid of greatest concern with regards to aquatic life toxicity, consistent with prior studies elsewhere. Toxicity to Hyalella azteca and/or Chironomus dilutus was found in two sediment samples at standard testing temperature (23 °C), and in one additional sample at a more environmentally realistic temperature (13 °C). Given the temperature dependency of pyrethroid toxicity, low temperatures typical of northwest streams can increase the potential for toxicity above that indicated by standard testing protocols.