title: Toxicity of atrazine to the juvenile hard clam, Mercenaria mercenaria.
abstract: The herbicide atrazine is one of the most heavily used pesticides in the United States. The effects of atrazine on the clam Mercenaria mercenaria were evaluated in aqueous and sediment laboratory assays. Juvenile clams of approximately 1mm in size were used for all experiments. An acute aqueous bio-assay was used to determine the 96-h LC(50) for the juvenile clams. A chronic aqueous bioassay was conducted at lower atrazine concentrations over a 10-day exposure period to examine both lethal and sublethal (dry mass, shell size, and condition index) endpoints. A chronic sediment bioassay examined mortality and sublethal endpoints in a 10-day exposure. The acute 96-h LC(50) was 5608 microg/L with 95% confidence intervals ranging from 5003 to 6287 microg/L. Results of the chronic aqueous assay indicated both lethal and sublethal (reduced shell size) effects at high atrazine concentrations. In the 10-day chronic aqueous assay, the no observable effect concentration was 500 microg/L, the lowest observable effect concentration was 1000 microg/L, and the maximum allowable toxicant concentration (MATC) was 707 microg/L. There were no significant effects of atrazine in the chronic sediment exposure. Safe concentrations for the aqueous experiments were estimated by applying an uncertainty factor of 10 to the calculated MATC values. While there were adverse effects of atrazine at high concentrations, these results suggest that atrazine is not directly toxic to M. mercenaria at environmentally relevant concentrations.
authors.affiliation: Office of Response and Restoration, National Oceanic and Atmospheric Administration, 77 West Jackson SR_6J, Chicago, IL 60604, USA.
authors.forename: Jennifer C
authors.initials: JC
authors.lastname: Lawton
authors.forename: Paul L
authors.initials: PL
authors.lastname: Pennington
authors.forename: Katy W
authors.initials: KW
authors.lastname: Chung
authors.forename: Geoffrey I
authors.initials: GI
authors.lastname: Scott
mesh_terms: D000818:Animals; D001280:Atrazine / Q000633:toxicity*; D019015:Geologic Sediments; D006540:Herbicides / Q000633:toxicity*; D007928:Lethal Dose 50; D049891:Mercenaria / Q000187:drug effects* / Q000502:physiology; D019055:No-Observed-Adverse-Effect Level; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D006540:Herbicides; D014874:Water Pollutants, Chemical; D001280:Atrazine