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Atrazine is a widely used herbicide in the US found at levels ranging from10 ng/L to 62.5 microg/L in estuaries throughout the southeast. Effects of atrazine on estuarine meiobenthic assemblages chronically exposed to environmentally relevant concentrations are unknown. The purpose of our research was to assess effects of atrazine on meiobenthos at concentrations near the proposed USEPA SWQC (26 microg/L) using modular estuarine salt marsh mesocosms as a field surrogate. Indigenous copepod and nematode densities were assessed after 28 days of exposure in transplanted colonization chambers. Cluster analysis showed a group characterized by low copepod densities, mostly atrazine exposed chambers, and a group containing all but one control chamber. The later group included chambers with high densities of the copepods Paronychocamptus wilsoni and Enhydrosoma baruchi. Compared to controls, copepod densities was approximately 70% lower in atrazine chambers, with three of the most common copepod species (E. baruchi, Onychocamptus sp. and P. wilsoni) showing an average of 50-70% reduction in population densities (p0.05). Although nematode density did not differ between atrazine and control chambers, the nematode-to-copepod ratio was significantly higher in atrazine (9.95+/-7.61; p=0.011) than in control chambers (0.61+/-0.35). Our findings suggest that chronic exposures over multiple generations to atrazine at concentrations near the proposed USEPA SWQC could have significant effects on the abundance and composition of estuarine meiobenthic copepod assemblages.

Coastal urbanization supplies surrounding estuarine environments with urban-related contaminants such as polycyclic aromatic hydrocarbons (PAHs), metals and pesticide mixtures. In our study, adult female and male copepods (Amphiascus tenuiremis) were chronically exposed to 18 sediment samples collected from sites influenced by different land-uses. Sediment samples were collected from three major suburban areas (Hilton Head, Kiawah Island and the Okatee River watershed) and a pristine site (North Inlet) in coastal South Carolina. Three-sediment bioassays (six sites per bioassay) were conducted by culturing copepods for 14 days in quadruplicate test sediments under flow-through conditions at 20 � C and 12:12 LD cycles. Adult survival and copepod reproductive output were quantified. Sediment samples were also analyzed by GC–MS for low and high molecular weight PAHs. Minimal adult mortality was observed in most sediment samples. However, sediments from Hilton Head Island and the Okatee River showed significant effects on copepod reproductive output (i.e., nauplii, copepodites and clutch size). Thus, we determined that reproductive endpoints rather than adult copepod survivorship were more sensitive to effects of contaminated sediments on A. tenuiremis. Furthermore, six (33%) of the 18 sites had a >25% reduction in copepod bioassay endpoints relative to controls, suggesting a high risk to long term A. tenuiremis population maintenance. � 2004 Elsevier Ltd. All rights reserved.

We compared a 21 day full life-cycle bioassay with an existing 14 day partial life-cycle bioassay for two species of meiobenthic copepods, Microarthridion littorale and Amphiascus tenuiremis. We hypothesized that full life-cycle tests would better simulate chronic exposures to copepods and provide more sensitive and realistic information about contaminant effects on growth of copepod populations. Copepods were exposed to sediments from two sites, non-contaminated North Inlet Estuary (NIE), SC (USA), and highly contaminated Shipyard Creek (SYC), SC, and measured for lethal and sublethal test points. Fourteen and 21 day bioassays showed similar negative effects in SYC sediments for both species. Survival and reproductive success were higher in the 14 day than in the 21 day bioassay for both species, in both sediment types. The lower 21 day overall response was not indicative of enhanced bioassay sensitivity. The 14 day bioassay provides sufficient f 1 generation information to detect negative population level responses to contaminant mixtures.