Pyrethroids In Sediment Research Articles

Development of film-based passive samplers for in situ monitoring of trace levels of pyrethroids in sediment

Residues of pyrethroid insecticides tend to accumulate in bed sediments due to their strong hydrophobicity. Rather than the total or bulk sediment concentration, it is the freely dissolved concentration (Cfree) that drives toxicity to benthic invertebrates. In this study we developed thin film-based samplers for in situ ambient monitoring of pyrethroids at trace levels in sediment. Out of five common polymer materials, polyethylene (PE) and silicone rubber (SR), were identified to offer superior enrichment for pyrethroids from sediment. To circumvent the slow equilibrium process, 13C-permethrin and bifenthrin-d5 were preloaded onto the films as performance reference compounds (PRCs). The PRC-preloaded film samplers were deployed at five sites in Southern California under field conditions for 7 d and retrieved for analysis. The sediment porewater Cfree of eight pyrethroids derived from PRC-PE films ranged from 173 to 903 ng/L, accounting for 18.2–36.1% of the corresponding total porewater concentrations. The PRC-SR film samplers yielded Cfree values closely mimicking those from the PRC-PE samplers, cross-validating the two sampling devices. Additionally, a significant positive association was found between the observed mortality from toxicity tests using Hyalella azteca and the Cfree of bifenthrin (r = 0.628, p = 0.02). A significant linear correlation (R2 = 0.99) between Cfree derived from in situ monitoring and that of ex situ measurement under equilibrium conditions was also observed. Results from this study demonstrated that the film-based samplers may be used for in situ ambient monitoring to detect biologically relevant contamination of pyrethroids in bed sediments, which may contribute to improved risk assessment for this class of widely used insecticides.

Methodological and Environmental Impacts on Bioaccessibility Estimates Provided by Single-Point Tenax Extractions.

Single-point Tenax extractions (SPTEs) of hydrophobic organic contaminants provide estimates of bioaccessibility through consistent measures of the chemical concentration initially in the rapidly desorbing fraction in sediment (C rapT0), such that a constant ratio is expected between SPTE and C rapT0 (C T /C rapT0, where T is the duration of the SPTE). As environmental factors (i.e., aging time and organic carbon content) and contaminant hydrophobicity can affect the C rapT0, the utility of the SPTEs as exposure estimates hinges on the consistency of the C T /C rapT0 ratio. Individually these factors have little impact on the ability of SPTEs to represent bioaccumulation, but the effect of these factors in combination, as well as SPTE methodological variation on the C T /C rapT0 ratio is poorly understood. The current study evaluated how environmental and methodological variation-expressed as varying Tenax to organic carbon mass (Tenax:OC) ratios-impacts the C 24h/C rapT0 ratio of pyrethroids in laboratory-spiked sediments. A multiple regression analysis was used to examine the impact of organic carbon, pyrethroid hydrophobicity, Tenax mass, and aging time on the C 24h/C rapT0 ratio. Only aging time of the pyrethroids in sediment significantly affected the C 24h/C rapT0 ratio with a slight decline of -0.0027/d in the C 24h/C rapT0 ratio, and this decline was considered negligible as a consistent C 24h/C rapT0 ratio of 1.46±0.03 was observed across all experimental treatments. This result further demonstrates the consistency of SPTEs to estimate bioaccessibility of hydrophobic contaminants in sediment and subsequent exposure.

The relationship of benthic community metrics to pyrethroids, metals, and sediment characteristics in Cache Slough, California

ABSTRACTA bioassessment multiple stressor study was conducted at 12 sites in Cache Slough, California during the Spring and Fall of 2012, 2013 and 2014. Specific study goals were to: (1) collect and identify benthic macroinvertebrates and develop a suite of benthic metrics; (2) measure total organic carbon (TOC), grain size, bulk metals, simultaneously extracted metals (SEM) and acid volatile sulfides (AVS), and 8 pyrethroids in sediment; (3) measure basic water quality parameters; and, (4) use univariate and stepwise multiple regressions and canonical correlation analysis to determine the relationship between various benthic metrics (i.e., taxa richness, abundance) and TOC, grain size, metals (bulk metals and SEM/AVS) and pyrethroids using the 3-year database. Five benthic metrics showed statistically significant relationships with environmental variables. Taxonomic Richness, a metric that decreases with stress, tended to be greater in less organic-rich, coarser sediments and the apparent relationships with toxicants such as pyrethroids or metals were diminished when these conditions are taken into account. The % Amphipod metric, which has a variable response to environmental stressors, showed a direct relationship with arsenic, an inverse relationship with chromium and an inverse relationship with % silt. The % Corbicula metric, which has a variable response to environmental stressors, was directly correlated with cypermethrin and nickel. Therefore, it appears that Corbicula tends to be associated with more contaminated sediments in Cache Slough. The metric % Collectors/Filterers & Collectors/Gatherers, a metric that increases in stressed environments, was reported to increase in sediments with higher arsenic concentrations. This relationship makes ecological sense because this metric should increase with an increase in arsenic concentrations. The benthic metric Abundance, a metric that decreases with stress, was reported to be inversely correlated with % TOC and % silt. The abundance of benthic communities increases in coarser, less organic rich sediments. In general, relatively few statistically significant relationships were observed between the various combinations of benthic metrics and environmental variables. Benthic communities in Cache Slough appear to be more closely associated with sediment characteristics and with metals concentrations than with the pyrethroid concentrations.

Organic carbon content effects on bioavailability of pyrethroid insecticides and validation of Solid Phase Extraction with Poly (2,6-diphenyl-p-phenylene oxide) Polymer by Daphnia magna toxicity tests

Solid phase extraction with Poly (2,6-diphenyl-p-phenylene oxide) Polymer (Tenax) was used for determining the bioavailability of eleven pyrethroids in field collected sediments with different organic carbon content (OC). The bioavailable fraction of pyrethroids decreased with increasing OC in sediments; the percentages of desorption ranged from 10 to 20% for sediment with higher OC content (5.8%) and 15–40% for that with lower OC (2%). Generally pyrethroids showed low bioavailability and cyfluthrin resulted to be the most bioavailable among the studied pyrethroids. Acute toxicity tests with Daphnia magna were carried out on sediment spiked with three selected pyrethroids (λ-cyhalothrin, cypermethrin and deltamethrin) and served to validate the efficiency of Tenax as a method for assessing the bioavailability of pyrethroids. Toxicity test demonstrated that Tenax was able to remove the toxic bio-available fraction of pyrethroids in sediment. Extracts from Tenax beads after the desorption experiments and spiked sediment before desorption had an equivalent toxicity (LC50) to D. magna neonates at 48 and 72h of exposure. These results indicate that Tenax beds can be used to predict bio-available and toxic fractions of pyrethroids sorbed to sediments to aquatic organisms like D. magna.

Mapping the Spatial Extent of Depositional Areas in Agricultural, Urban, and Residential California Streams: Implications for Pyrethroid Toxicity

ABSTRACT Wetted stream-bed mapping at randomly selected sites in an agricultural stream (Del Puerto Creek), urban stream (Arcade Creek), and residential stream (Pleasant Grove Creek) in California was conducted to determine the spatial extent of depositional and non-depositional areas. This study evaluated the “representativeness” of standard sediment sampling approaches used in California by using hydrophobic pyrethroids as an example. Measured background concentrations of eight pyrethroids in sediment and potential sediment toxicity for each stream were discussed within the context of depositional areas. Four percent, 15%, and 12% of the randomly selected transects in Del Puerto Creek, Arcade Creek, and Pleasant Grove Creek, respectively, were depositional areas. For all three streams, depositional areas were more dominant in downstream segments. Pyrethroid concentrations in sediment were higher in depositional areas versus non-depositional areas in Del Puerto Creek and were also higher downstream. Pyrethroid concentrations in sediment were also higher in downstream areas of Arcade Creek but generally higher in upstream areas of Pleasant Grove Creek. The results from this study demonstrate the importance of determining “representativeness” of depositional areas for an entire stream if hydrophobic chemicals (pyrethroids) measured in sediment from depositional areas are suspected to be toxic.

Environmental fate of pyrethroids in urban and suburban stream sediments and the appropriateness of Hyalella azteca model in determining ecological risk

According to several recent studies using standard acute Hyalella azteca sediment bioassays, increased pyrethroid use in urban and suburban regions in California has resulted in the accumulation of toxic concentrations of pyrethroids in sediments of area streams and estuaries. However, a critical review of the literature indicates that this is likely an overestimation of environmental risk. Hyalella azteca is consistently the most susceptible organism to both aqueous and sediment-associated pyrethroid exposures when compared to a suite of other aquatic taxa. In some cases, H. azteca LC50 values are less than the community HC10 values, suggesting that the amphipod is an overly conservative model for community- or ecosystem-level impacts of sediment-associated pyrethroids. Further, as a model for responses of field populations of H. azteca, the laboratory bioassays considerably overestimate exposure, because the amphipod is more appropriately characterized as an epibenthic organism, not a true sediment dweller; H. azteca preferentially inhabit aquatic macrophytes, periphyton mats, and leaf litter, which drastically reduces their exposure to contaminated sediments. Sediment-bound pyrethroids are transported via downstream washing of fine particulates resulting in longer range transport but also more efficient sequestration of the chemical. In addition, site-specific variables such as sediment organic carbon content, grain size, temperature, and microbial activity alter pyrethroid bioavailability, degradation, and toxicity on a microhabitat scale. The type and source of the carbon in particular, influences the pyrethroid sequestering ability of sediments. The resulting irregular distribution of pyrethroids in stream sediments suggests that sufficient nonimpacted habitat may exist as refugia for resident sediment-dwelling organisms for rapid recolonization to occur. Given these factors, we argue that the amphipod model provides, at best, a screening level assessment of pyrethroid impacts and can correctly identify those sediments not toxic to benthic organisms but cannot accurately predict where sediments will be toxic.

Occurrence and distribution of sediment-associated insecticides in urban waterways in the Pearl River Delta, China

Sediment-associated pesticides, including organochlorine (OCP), organophosphate (OP), and pyrethroid insecticides, were analyzed in urban waterways in three cities (Guangzhou, Dongguan, and Shenzhen) in the Pearl River Delta (PRD), China. The OCPs represented 27.2% of the detectable insecticides in sediment, and chlordanes, DDTs, and endosulfans were the most frequently detected OCPs. The currently used insecticide chlorpyrifos was the only OP detected above the reporting limit (RL), with concentrations ranging from <RL to 100 ng g −1 dry weight (dw). Additionally, pyrethroids were detected in all sediments with the sum pyrethroid concentrations ranging from 4.26 to 384 ng g −1 dw and this represented 64.9% of the sum insecticide concentration. Despite their widespread use, no studies have been conducted investigating the occurrence and distribution of pyrethroids in China. As the first report of pyrethroids in urban waterways in China, the current study found cypermethrin was the most abundant insecticide detected in the PRD at concentrations ranging from 1.44 to 219 ng g −1 dw. Spatially, sediment from more populous and urbanized areas (Shenzhen and Tianhe district in Guangzhou) had higher insecticide residues than less populous agricultural areas. In the more modernized city of Shenzhen, the OCPs were seldom detected, whereas more diverse patterns of pyrethroids were observed. Potential sources of these insecticides, especially the frequently detected pyrethroids, were most likely from pest control during urban landscaping maintenance and from abatement programs targeting mosquitoes and ants. Results suggested that a shift in application pattern and elevated urbanization increased accumulation of currently used insecticides like pyrethroids in sediment, and made them the predominate insecticides in the PRD urban waterways.

Effect of Dissolved Organic Carbon on Sorption of Pyrethroids to Sediments

Despite their strong hydrophobicity, recent studies showed widespread occurrence of pyrethroid in downstream surface waters bodies. In this work, the effect of dissolved organic carbon (DOC) on the sorption and desorption of pyrethroids in sediment was evaluated to understand the role of DOC in facilitating pyrethroid transport. Presence of DOC from three sources at 38 ± 2 mg L⁻¹ in the aqueous phase decreased pesticide sorption to a sediment by 1.7 to 38.9 times and increased their desorption by 1.2 to 41.4 times. The effect on pyrethroid sorption to the sediment was linear. In addition, interactions between DOC and pyrethroids, when taking place prior to the contact with sediment, decreased sorption of some pyrethroids even further, implying that DOC-pyrethroid complexs were relatively stable in solution. DOC sources with higher contents of carboxylic and phenolic groups were found to have a higher potential to associate with pyrethroids. The DOC-water partition coefficients (K(DOC)) obtained by solid-phase microextraction measurement were significantly correlated (P < 0.01) with K(d) values measured for the sediment. These results provide evidence that DOC increases the distribution of pyrethroids from the sediment to the solution phase and plays an important role in mobilizing pyrethroids in runoff and surface streams.

MEASURING PYRETHROIDS IN SEDIMENT PORE WATER USING MATRIX-SOLID PHASE MICROEXTRACTION

Pyrethroids are hydrophobic insecticides commonly used in both agricultural and urban environments. Their high toxicity to aquatic organisms, including benthic invertebrates, and detection in the sediment at many locations in California, U.S.A., have spawned interest in understanding their bioavailability in bed sediments. A recent study showed good correlation between uptake of 14C-permethrin in Chironomus tentans and solid-phase microextraction (SPME) fibers in sediments. The present study was directed at the development of an SPME technique applicable to trace levels of nonlabeled pyrethroids in sediment. Disposable polydimethylsiloxane fibers were used to detect freely dissolved pore-water concentrations of bifenthrin, fenpropathrin, cis-permethrin, trans-permethrin, cyfluthrin, cypermethrin, and esfenvalerate under agitated and static conditions. Partition equilibrium between fiber and sediment was reached in <5 d when the samples were agitated on a shaker at low speed, while much longer times (>23 d) were needed without agitation. Polydimethylsiloxane to water partition ratios (K(PDMS)) of the seven pyrethroids were measured separately and ranged from 2.83 x 10(5) to 1.89 x 10(6). When applied to field-contaminated sediments, agitated matrix-SPME was able to detect pore-water concentrations as low as 0.1 ng/L. The method developed in the present study may be coupled with bioassays to gain mechanistic understanding of factors affecting pyrethroid toxicities, and applied to field samples to better predict sediment toxicities from pyrethroid contamination.

Effects of Black Carbon on Pyrethroid Availability in Sediment

Pyrethroids are widely used synthetic insecticides with the characteristics of high hydrophobicity and broad-spectrum aquatic toxicity. Many studies indicate that black carbon (BC) plays an important role in the bioavailability of hydrophobic compounds such as polycyclic aromatic hydrocarbons and polychlorinated biphenyls in soils and sediments. However, the effect of BC on bioavailability of other compounds such as pyrethroids in sediments is less known. In this study, we simultaneously measured pyrethroid uptake into polydimethylsiloxane (PDMS) fibers and 24 h bioaccumulation in Chironomus tentans in a sediment amended with a charcoal at different rates. There were significant negative correlations between the accumulation of pyrethroids in PDMS fibers (C(PDMS)) and the charcoal level in sediment. When the charcoal content was increased from 0 to 1.0%, C(PDMS) decreased by 5.7-9.1%. Amendment of 1.5% charcoal to the original sediment decreased biota sediment accumulation factor (BSAF) of (14)C-permethrin in C. tentans from 2.8 to 1.7. The effect of charcoal was further found to be similar for the different subcellular fractions of C. tentans, including cell debris, organelles and proteins, and granules. The overall effect of charcoal on pyrethroid availability, however, was modest, and adsorption of pyrethroids on pure charcoal was found to be similar to that on sediment organic carbon. The relatively weak sorption on charcoal was likely due to the large molecular weight and sizes of pyrethroids, which might hinder their diffusion into charcoal nanopores.

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.