Rising seas and roadway debris: Microplastic and low-density tire wear particles in street-associated tidal floodwater.

Tidal flooding is increasingly common in low-lying coastal regions as sea levels rise. This type of flooding can occur on sunny days with no rainfall and may transport street-associated debris, such as microplastics (MPs) including tire wear particles (TWPs), to coastal systems. This research aimed to quantify MP abundance in tidal floodwater and investigate their fate. Three locations around Charleston, SC (USA) were sampled during 12 tidal floods, and their adjacent tidal creeks were sampled before and after 5 floods. Floodwater contained an average of 342 ± 60 MP/L. Most MPs in floodwater were low-density TWP (86.5 %). MP abundance in tidal creek surface water following flooding did not change, suggesting that MPs were not immediately transferred to coastal waterways but deposited in adjacent marsh sediment. Elucidating transport routes of MPs in coastal environments is critical to understanding and preventing this type of contamination in the face of a changing climate.

Spatial and temporal variability of microplastic abundance in estuarine intertidal sediments: Implications for sampling frequency.

Microplastics (<5 mm) are well documented across shorelines worldwide; however, high variability in microplastic abundance is often observed within and among field studies. The majority of microplastic surveys to date consist of single sampling events that do not consider spatiotemporal variability as a potential confounding factor in the interpretation of their results. Therefore, these surveys may not accurately capture or reflect levels of microplastic contamination in the environment. Here, we provide the first investigation of small-scale spatial and temporal variability of microplastic abundance, distribution, and composition in the intertidal zone of an urbanized US estuary to better understand the short-term, daily spatiotemporal variability of microplastics in dynamic coastal environments. Intertidal sediment was collected from both the low and high intertidal zones of a sandy estuarine beach located in South Carolina, southeastern US every 1 to 2 days at low tide over 17 days (12 sampling events; total n = 72). Study-wide, microplastic abundance ranged from 44 to 912 microplastics/m2 and consisted primarily of polyethylene, nylon, polyester, and tire (or tyre) wear particles. High temporal variability was observed, with microplastic abundance differing significantly among sampling events (p = 0.00025), as well as among some consecutive tidal cycles occurring within 12 h of each other (p = 0.007). By contrast, low spatial variability was observed throughout the study with no significant differences in microplastic abundance detected between the low and high intertidal zones (p = 0.76). Of the environmental factors investigated, wind direction on the day of sampling had the greatest effect on temporal microplastic variability. Our results demonstrate that there can be significant temporal variability of microplastic abundance in estuarine intertidal sediments and are important for informing the methods and interpretation of future microplastic surveys in dynamic coastal environments worldwide.

Are Green Household Consumer Products Less Toxic than Conventional Products? An Assessment Involving Grass Shrimp (Palaemon pugio) and Daphnia magna.

Although it is generally assumed that green household consumer products (HCPs) contain individual compounds that are less toxic and/or more degradable than conventional HCPs, little research on this topic has been conducted. In our assessments, larval grass shrimp (Palaemon pugio) were used in a biodegradation study and juvenile freshwater cladocerans, Daphnia magna, were used in a photodegradation study. In each study, organisms were exposed to nondegraded and degraded treatments consisting of one green HCP and two conventional HCPs in six different categories (laundry detergent, dish detergent, mouthwash, insecticide, dishwasher gel, and all-purpose cleaner). Sensitivity to these products were assessed using 48-h static acute toxicity tests, and the median lethal concentrations (LC50s) then compared using an LC50 ratio test. For grass shrimp, only one green HCP (insecticide) was less toxic than both conventional HCPs. In one category (laundry detergent), the green HCP was the more toxic than either conventional HCP. Following a biodegradation treatment, none of the green product formulations became less toxic, whereas 44.4% of the conventional HCPs demonstrated decreased toxicity. For daphnids, green HCPs in three categories (dish detergent, insecticide, and all-purpose cleaner) were less toxic than both conventional products tested. Following a photodegradation treatment, two green product formulations (dish detergent and dishwasher gel) became less toxic (33.3%), whereas 87.5% of the conventional HCPs demonstrated decreased toxicity. The present study demonstrates that green HCPs are not necessarily less toxic and/or more degradable than their conventional counterparts. These results also suggest that the toxicity and degradability of end-product formulations need to be considered in the overall framework for green product evaluation. Environ Toxicol Chem 2022;41:2444-2453. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Accumulation and depuration of microplastic fibers, fragments, and tire particles in the eastern oyster, Crassostrea virginica: A toxicokinetic approach.

Along the South Carolina coast (U.S.) where the ecologically and economically important eastern oyster (Crassostrea virginica) forms extensive intertidal reefs, recent surface water surveys found that fibers, fragments, and microscopic tire particles represented 43.6%, 30.9%, and 17.7% of the total microplastics, respectively. The aim of this study was to characterize accumulation and depuration of these particles in eastern oysters. Oysters were exposed to purple polyethylene fibers, green nylon fragments, or micronized crumb rubber at a concentration of 5000 microplastics/L, and sacrificed after 0, 24, 48, and 96 h to characterize uptake. Following 96 h, remaining oysters were transferred to microplastic-free brackish water and sacrificed at 24, 48, and 96 h to characterize depuration. For fibers and fragments, levels increased in a nonlinear fashion reaching 1.61 ± 0.6 particles/g w. w. (mean ± SE) and 0.46 ± 0.1 particles/g w. w. after 96 h, respectively. Conditional uptake clearance rate constants (ku) were estimated to be 0.0084 and 0.0025 mL/g*h for fibers and fragments, respectively. For crumb rubber, levels increased in a linear fashion reaching 3.62 ± 0.8 particles/g w. w. after 96 h, and the ku value was estimated to be 0.0077 mL/g*h. Depuration was best described using a two-compartment (double exponential) model suggesting the presence of fast and slow compartments. Conditional depuration rate constants (kd) for the slow compartments were 0.0084, 0.0205, and 0.0048/h for fibers, fragments, and crumb rubber, respectively. These results demonstrate accumulation and depuration of microplastics in eastern oysters is size-and shape-dependent. Depuration, which is a common practice for shellfish safety, is an effective way to reduce microplastic loads in eastern oysters, but the minimum recommended time of 44 h would only reduce loads of these particles by 55.5-67.6%.

Assessment of acute toxicity and developmental transformation impacts of polyethylene microbead exposure on larval daggerblade grass shrimp (Palaemon pugio).

Due to the ubiquity of microplastic contamination in coastal waters, there is potential for adverse impacts to organism development. One organism of interest is the daggerblade grass shrimp, Palaemon pugio, an ecologically important species in estuaries along the east coast of North America. We exposed larval grass shrimp to virgin polyethylene microbeads (35 and 58 µm) at a high (0.375 and 1.95 mg/L), medium (0.0375 and 0.195 mg/L), and a low concentration (0.00375 and 0.0195 mg/L), respectively for 23 days to assess mortality, transformation time from larval to juvenile stage, and weight. Average percent mortality was 3.7 to 4.8 times higher in the experimental treatments compared to controls. The greatest proportion of mortality was observed in the first 11 days. Median time for transformation ranged from 20.2 to 20.8 days. Shrimp exposed to the 35 µm beads in the high treatment (20.2 days) transformed significantly faster than the control shrimp (20.8 days). Although development was not delayed and size of the shrimp did not differ, the acute toxicity of microplastics on grass shrimp is a concern due to their role in energy cycling within tidal-creeks. These findings suggest potential population and community level effects following microplastic exposure.

Degradation of bio-based and biodegradable plastics in a salt marsh habitat: Another potential source of microplastics in coastal waters.

Degradation of bio-based (polylactic acid [PLA] cups, Mater-Bi® [MB] bags) and biodegradable plastics (biodegradable extruded polystyrene [bioPS] plates, biodegradable high density polyethylene [bioHDPE] bags) were compared to conventional plastics (recycled polyethylene terephthalate [rPET] cups, HDPE bags, extruded PS plates) in a salt marsh over a 32-week period. Following 4 weeks, biofilm developed on all plastics, resulting in an increased weight and concomitant decrease in UV transmission for most plastics. All plastics produced microplastic particles beginning at 4 weeks, with single-use bags producing the most microplastics over the 32-week period. At 32 weeks, SEM revealed microcracks and delamination for all plastics except PLA and MB, the latter of which degraded through embrittlement. IR spectral analysis indicated degradation for all plastics except PLA. Results suggest that degradation rates of bio-based and biodegradable plastics vary widely, with MB bags and bioPS plates demonstrating the greatest degradation, while PLA cups demonstrated the least degradation.

Microplastic and tire wear particle occurrence in fishes from an urban estuary: Influence of feeding characteristics on exposure risk.

The influence of feeding behavior and feeding ecology on microplastic occurrence in fishes in an urbanized estuary was studied by surveying microplastics in the digestive tracts (gut) of five fish species: the planktivorous Bay Anchovy and Atlantic Menhaden, the piscivore Spotted Seatrout, the benthivore Spot and the detritivore/benthivore Striped Mullet. Microplastics were found in 99% of fishes collected with an average of 27 microplastics per individual fish, 6 microplastics per gram of fish, and 21 microplastics per gram of gut, although exposure varied among species. Atlantic Menhaden possessed significantly more microplastic per fish weight than other species, which may be attributed to their regular ingestion of marine snow aggregates. Fibers were the most common type of microplastic in all fishes, and suspected tire wear particles were found in 14% of individuals across all five species, constituting the first evidence of tire wear particle consumption in field-collected organisms.

Occurrence of tire wear particles and other microplastics within the tributaries of the Charleston Harbor Estuary, South Carolina, USA.

Microplastics (<5 mm) are ubiquitous in the marine environment, occurring in both sediments and surface waters worldwide. However, few studies have documented the presence of microplastics and tire wear particles in coastal rivers. A survey of microplastics and low-density tire wear particles (≥63 µm) in the sediment and surface water of the three major tributaries within the Charleston Harbor estuary was conducted. Intertidal sediment, subtidal sediment, and sea surface microlayer concentrations ranged from 0 to 652 microplastics/m2, 3-4,375 microplastics/kg wet weight, and 3-36 microplastics/L, respectively. Blue fibers and tire wear particles were the two most abundant microplastic types observed, constituting 26.2% and 17.1%, respectively, of total microplastics. Tire wear particles were primarily identified by morphology, and ATR-FTIR analysis was conducted for a small subset (n = 5) of larger particles (≥500 µm). The present study provides the first microplastic field assessment of low-density tire wear particles in estuarine tributaries.

The Effect of Microplastic Ingestion on Survival of the Grass Shrimp Palaemonetes pugio (Holthuis, 1949) Challenged with Vibrio campbellii.

Recent research indicates that microplastic (<5 mm) ingestion may impact the immune function of marine and aquatic organisms at the tissue and cellular levels; however, their susceptibility to disease following exposure has not been directly investigated. The objective of the present study was to directly evaluate the impact of microplastic ingestion on the susceptibility of the grass shrimp Palaemonetes pugio to bacterial infection with Vibrio campbellii. Grass shrimp were exposed to one of several particle treatments (natural sediment, polyethylene spheres, polypropylene fragments, tire fragments, and polyester fibers) or particle-free water for 96 h at a nominal concentration of 50 000 particles/L prior to a bacterial challenge with V. campbellii. No significant mortality was observed among any of the particle types during the 96-h particle exposure. The survival of grass shrimp following V. campbellii challenge did not vary significantly among shrimp exposed to particle-free water, sediment, polyethylene spheres, polypropylene fragments, tire fragments, and polyester fibers. Grass shrimp cleared the majority of ingested particles and all the ventilated particles within 48 h. The present study shows that microplastic ingestion did not alter the susceptibility of grass shrimp to bacterial infection, and also provides depuration rates for a variety of microplastic shapes and polymer types that were previously lacking. This information increases our understanding of the size- and shape-dependent effects of microplastic ingestion. Environ Toxicol Chem 2019;38:2233-2242. © 2019 SETAC.

Microplastic in two South Carolina Estuaries: Occurrence, distribution, and composition.

Here we report on the distribution of microplastic contamination in two developed estuaries in the Southeastern United States. Average concentration in intertidal sediments of Charleston Harbor and Winyah Bay, both located in South Carolina, U.S.A., was 413.8 ±â€¯76.7 and 221.0 ±â€¯25.6 particles/m2, respectively. Average concentration in the sea surface microlayer of Charleston Harbor and Winyah Bay was 6.6 ±â€¯1.3 and 30.8 ±â€¯12.1 particles/L, respectively. Concentration in intertidal sediments of the two estuaries was not significantly different (p = 0.58), however, Winyah Bay contained significantly more microplastics in the sea surface microlayer (p = 0.02). While microplastic concentration in these estuaries was comparable to that reported for other estuaries worldwide, Charleston Harbor contained a high abundance of black microplastic fragments believed to be tire wear particles. Our research is the first to survey microplastic contamination in Southeastern U.S. estuaries and to provide insight on the nature and extent of contamination in these habitats.

Size- and shape-dependent effects of microplastic particles on adult daggerblade grass shrimp (Palaemonetes pugio).

The incidence of microplastics in marine environments has been increasing over the past several decades. The objective of the present study was to characterize the size- and shape-dependent effects of microplastic particles (spheres, fibers, and fragments) on the adult daggerblade grass shrimp (Palaemonetes pugio). Grass shrimp were exposed to 11 sizes of plastic: spheres (30, 35, 59, 75, 83, 116, and 165 µm), fragments (34 and 93 µm), and fibers (34 and 93 µm) at a concentration of 2000 particles/400 mL (= 50 000 particles/L) for 3 h. Following exposure, grass shrimp were monitored for survival, ingested and ventilated microplastics, and residence time. Mortality ranged from 0% to 55%. Spheres and fragments <50 µm were not acutely toxic. Mortality rates in experiments with spheres and fragments >50 µm ranged from 5% to 40%. Mortality was significantly higher in the exposure to 93-µm fibers than other sizes tested (p < 0.001). The shape of the particle had a significant influence on the number of particles ingested by the shrimp (p < 0.001). The residence time of particles in the gut ranged from 27 to 75 h, with an average of 43.0 ± 13.8 h. Within the gills, the residence time ranged from 27 to 45 h, with an average of 36.9 ± 5.4 h. The results suggest that microplastic particles of various sizes and shapes can be ingested and ventilated by adult daggerblade grass shrimp, resulting in acute toxicity. Environ Toxicol Chem 2017;36:3074-3080. © 2017 SETAC.

Trophic transfer of microplastics in aquatic ecosystems: Identifying critical research needs.

To evaluate the process of trophic transfer of microplastics, it is important to consider various abiotic and biotic factors involved in their ingestion, egestion, bioaccumulation, and biomagnification. Toward this end, a review of the literature on microplastics has been conducted to identify factors influencing their uptake and absorption; their residence times in organisms and bioaccumulation; the physical effects of their aggregation in gastrointestinal tracts; and their potential to act as vectors for the transfer of other contaminants. Limited field evidence from higher trophic level organisms in a variety of habitats suggests that trophic transfer of microplastics may be a common phenomenon and occurs concurrently with direct ingestion. Critical research needs include standardizing methods of field characterization of microplastics, quantifying uptake and depuration rates in organisms at different trophic levels, quantifying the influence that microplastics have on the uptake and/or depuration of environmental contaminants among different trophic levels, and investigating the potential for biomagnification of microplastic-associated chemicals. More integrated approaches involving computational modeling are required to fully assess trophic transfer of microplastics. Integr Environ Assess Manag 2017;13:505-509. © 2017 SETAC.

From macroplastic to microplastic: Degradation of high-density polyethylene, polypropylene, and polystyrene in a salt marsh habitat.

As part of the degradation process, it is believed that most plastic debris becomes brittle over time, fragmenting into progressively smaller particles. The smallest of these particles, known as microplastics, have been receiving increased attention because of the hazards they present to wildlife. To understand the process of plastic degradation in an intertidal salt marsh habitat, strips (15.2 cm × 2.5 cm) of high-density polyethylene, polypropylene, and extruded polystyrene were field-deployed in June 2014 and monitored for biological succession, weight, surface area, ultraviolet (UV) transmittance, and fragmentation. Subsets of strips were collected after 4 wk, 8 wk, 16 wk, and 32 wk. After 4 wk, biofilm had developed on all 3 polymers with evidence of grazing periwinkles (Littoraria irrorata). The accreting biofilm resulted in an increased weight of the polypropylene and polystyrene strips at 32 wk by 33.5% and 167.0%, respectively, with a concomitant decrease in UV transmittance by approximately 99%. Beginning at 8 wk, microplastic fragments and fibers were produced from strips of all 3 polymers, and scanning electron microscopy revealed surface erosion of the strips characterized by extensive cracking and pitting. The results suggest that the degradation of plastic debris proceeds relatively quickly in salt marshes and that surface delamination is the primary mechanism by which microplastic particles are produced in the early stages of degradation. Environ Toxicol Chem 2016;35:1632-1640. © 2016 SETAC.

Screening-level ecological and human health risk assessment of polycyclic aromatic hydrocarbons in stormwater detention pond sediments of Coastal South Carolina, USA.

Screening-level ecological and human health assessments were performed for polycyclic aromatic hydrocarbon (PAH) contamination in the sediments of 19 stormwater detention ponds located in coastal South Carolina. For ecological screening benchmarks, we used threshold and probable effect concentrations (TEC and PEC) derived from consensus-based sediment quality guidelines for individual PAH analytes and equilibrium partitioning sediment benchmarks-toxic units (SigmaESB-TU) derived for PAH mixtures. For human health benchmarks, we used preliminary remediation goals (PRGs). Sediments of five stormwater ponds (four commercial ponds and one residential pond with a large drainage area) exceeded PEC values for several PAH analytes and the SigmaESB-TU safe value of 1 for PAH mixtures. These same five stormwater ponds also exceeded the PRG values for five carcinogenic PAH analytes. These results suggest that the PAH levels in sediments from certain commercial and residential ponds have the potential to pose moderate to high risks for adverse, chronic effects to benthic organisms in situ and an increased risk of cancer to humans ex situ following excavation and on-site disposal. We recommend that sediment from these stormwater ponds be tested prior to excavation to determine the appropriate method of disposal. We also recommend that regulatory agencies enforce guidelines for periodic sediment removal as this should reduce both in situ and ex situ risks resulting from sediment PAH exposure.

A survey of metal and pesticide levels in stormwater retention pond sediments in coastal South Carolina.

During the summer of 2007, sediment samples were collected from 16 stormwater detention ponds and 2 reference ponds located in coastal South Carolina. The sediments were analyzed for more than 30 pesticides with current and historical uses, six polybrominated diphenyl ethers (PBDEs), and seven metals. The results are compared with established screening assessment parameters, with copper found to be the contaminant of highest concern. Lead levels were found to correlate well with pond drainage area, while copper and zinc levels correlated with both pond drainage area and pond surface area. Chlorpyrifos levels were found to correlate with pond surface area. Our results also show that ponds draining commercial areas were likely to have higher levels of zinc and lead in the sediments compared to other pond classes.

Polycyclic aromatic hydrocarbon contamination in stormwater detention pond sediments in coastal South Carolina.

The purpose of this study was to characterize the polycyclic aromatic hydrocarbon (PAH) contamination in the sediments of stormwater detention ponds in coastal South Carolina. Levels of the sum of PAH analytes were significantly higher in the sediments of commercial ponds compared to that of reference, golf course, low-density residential, and high-density residential ponds. Isomer ratio analysis suggested that the predominant source of PAHs were pyrogenic; however, many ponds had a PAH signature consistent with mixed uncombusted and combusted PAH sources. PAH levels in these sediments could be modeled using both pond drainage area and pond surface area. These results demonstrate that the sediment from most commercial ponds, and a few residential and golf course ponds, were moderately contaminated with PAHs. PAH levels in these contaminated ponds exceeded between 42% and 75% of the ecological screening values for individual PAH analytes established by US EPA Region IV, suggesting that they may pose a toxicological risk to wildlife.

Polycyclic aromatic hydrocarbon contamination in South Carolina salt marsh-tidal creek systems: relationships among sediments, biota, and watershed land use.

Sediments and biota from 11 tidal creeks were sampled and classified into forested, suburban, and urban/industrial watershed land-use categories. Total PAH levels ( summation operatorPAH(16)) in sediments were significantly higher in urban/industrialized creeks (5,795 +/- 1,173 ng/g) compared to suburban (793 +/- 131 ng/g) and forested (238 +/- 34 ng/g) creeks. No differences in summation operatorPAH(16) levels among land-use classifications were found for either oligochaetes (Monopylephorus rubroniveus) or grass shrimp (Palaemonetes pugio). However, summation operatorPAH(16) levels in grass shrimp were related to sediment summation operatorPAH(16) levels and summation operatorPAH(16) levels in oligochaetes and grass shrimp eggs were related to impervious cover in the watershed. Diagnostic ratios suggest that the primary sources of PAH in suburban and urban/industrialized creeks are pyrogenic. Carcinogenic PAH contents of sediments and biota were related to impervious cover. While human exposures to these sediment-associated carcinogens were not assessed, levels of several carcinogenic PAHs in sediments of urban/industrial tidal creeks were above the levels that represent an increased cancer risk in humans.

Survey of PAH in low density residential stormwater ponds in coastal South Carolina: false dark mussels (Mytilopsis leucophaeata) as potential biomonitors.

The distribution of PAHs was studied in sediment and false dark mussels, Mytilopsis leucophaeata, of three brackish stormwater retention ponds on Kiawah Island, a gated residential community and golf resort. Impervious surface in pond watersheds ranged from 5 to 30%. Sediment concentrations were lower than those found in other studies of suburban residential areas, and there were no significant differences among ponds or seasons. Mean summation PAH16 values for sediments in Ponds 67, 100, and 37 were 184.7+/-101.3ng g(-1), 67.5+/-26.0ng g(-1), and 84.3+/-75.5ng g(-1), respectively. Mussel summation PAH16 concentrations from Pond 67 in August (mean 734.5+/-148.1ng g(-1)), and from Pond 37 in December (mean 1115.1+/-87.7ng g(-1)), were significantly higher than other ponds. Mean summation PAH16 values for mussels in Ponds 67, 100, and, 37 were 555.9+/-219.7ng g(-1), 312.5+/-99.1ng g(-1) and 737.8+/-419.8ng g(-1), respectively. The mean biota-to-sediment ratio was 7.6+/-8.1. Isomer ratios generally suggested pyrogenic sources. False dark mussels are a promising indicator species for PAH contamination because they are abundant, easy to sample, bioaccumulate PAH profiles representative of the time-integrated sediment profiles, and their PAH levels are less variable than either stormwater or sediment samples.

Piperonyl butoxide enhances the bioconcentration and photoinduced toxicity of fluoranthene and benzo[a]pyrene to larvae of the grass shrimp (Palaemonetes pugio).

Piperonyl butoxide (PBO) is a commonly used synergist in many pyrethroid formulations due to its ability to interfere with cytochrome P450 (CYP) monooxygenases. Because PBO can co-occur in the estuarine environment with polycyclic aromatic hydrocarbons (PAHs), a class of compounds metabolized by CYP isozymes, the overall objective of this study was to investigate the influence of PBO on the bioconcentration and photoinduced toxicity of two common PAH contaminants, fluoranthene (FLU) and benzo[a]pyrene (BaP), on the larvae of the grass shrimp (Palaemonetes pugio). PBO alone was not particularly toxic to grass shrimp larvae. In dark exposures and under simulated sunlight (UV-A=211.0+/-7.0 microW/cm(2), UV-B=9.8+/-2.4microW/cm(2)), 96-h LC(50) values were similar (814.4 and 888.6 microg/L, respectively), suggesting that PBO toxicity is not enhanced in the presence of sunlight. The presence of sublethal concentrations of PBO in single PAH toxicity tests increased the bioconcentration of the two tested PAHs, and these increases were greatest at the lowest tested PAH concentrations. Mean bioconcentration factors (BCF) at the three lowest FLU and BaP treatments increased 14.3- and 7.1-fold, respectively, in the low PBO (127 microg/L) exposure compared to that of the no PBO exposure. Under simulated sunlight, PBO exposure also increased the photoinduced toxicity of the two tested PAHs, and this increase occurred in a PBO concentration-dependent fashion. For FLU, 96-h LC(50) values decreased from 2.35 microg/L in the absence of PBO to 0.76 microg/L in the high PBO (256 microg/L) exposure. For BaP, 96-h LC(50) values similarly decreased from 1.02 microg/L in the absence of PBO to 0.30microg/L in the high PBO exposure. The presence of PBO also influenced the PAH tissue residue-response relationship, but in different ways for FLU and BaP. For FLU, slopes of the tissue residue-response relationship decreased in the presence of PBO, and for BaP, there was a trend towards increased slopes in the presence of PBO. These results demonstrate that sublethal levels of PBO increase the bioconcentration and photoinduced toxicity of certain PAH in grass shrimp larvae, and underscore the need to consider the potential for PBO to synergize the toxicity of co-occurring environmental contaminants in future risk assessments.

Acute toxicity and acetylcholinesterase inhibition in grass shrimp (Palaemonetes pugio) and oysters (Crassostrea virginica) exposed to the organophosphate dichlorvos: laboratory and field studies.

The use of various organophosphates to control mosquito populations is a common practice across the globe. We review the literature (LC50s) on dichlorvos, the primary breakdown product of Dibrom, and use laboratory and field experiments to determine the lethal and sublethal (bioassays) effects of dichlorvos on two widely distributed and ecologically important estuarine invertebrate species, the marsh grass shrimp, Palaemonetes pugio and the Eastern oyster, Crassostrea virginica. Laboratory results based on LC50s and sublethal acetylcholinesterase (AChE) inhibition activity bioassays indicate that adult grass shrimp are more sensitive (approximately 500 x ) to dichlorvos than juvenile oysters. Although potentially an important factor for intertidal or shallow-dwelling estuarine organisms, the toxicity of dichlorvos was not enhanced in the presence of simulated sunlight for adult P. pugio. The most notable decreases in AChE activity were for grass shrimp and oysters exposed to dichlorvos concentrations above those considered ecologically relevant. In field experiments, both species were deployed in cages in unsprayed (n = 2) and sprayed (n = 3) sites and water samples collected pre- and post-spraying. Quantifiable dichlorvos levels were measured at the two narrowest creek treatment sites following mosquito spraying, suggesting that overspray can occur and there was evidence of a sublethal AChE response at these same sites. However, experiments at the widest creek revealed no measurable dichlorvos or sublethal responses. Results from this research suggest that adult grass shrimp are more sensitive to dichlorvos than juvenile oysters. Spraying near small tidal creeks may have measurable impacts on resident species, while larger (wider) creeks appear to be capable of buffering organisms from transient fluxes of mosquito control agents that may enter the system.