Subthreshold Toxic Effects of Atrazine and Three Degradates on Behavior in Procambarus clarkii

Atrazine is among the most heavily applied pesticides worldwide, and recent evidence suggests that it may be unsafe at environmental levels. It is a known endocrine disruptor and a suggested neurotoxin. The US EPA Maximum Contaminant Level (MCL) is 3 μg/L for human ingestion and 200 μg/L for limited human exposure. Several environmentally persistent degradates have been identified, including deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (HA). No MCLs have been established for these degradates, although some are suggested toxins. Thus, there remains concern for the risk associated with the presence of atrazine and its degradates in the environment. Currently little data exist describing sublethal effects of atrazine and its degradates. Fortunately, toxicological research has evolved past dependency on mortality measures to incorporate sophisticated behavioral studies that can elucidate the effects of sublethal exposure to toxins. The goal of this research was to use such parameters to quantify the subthreshold (below the level at which harm is immediately detected) toxic effects of atrazine, DEA, DIA and HA on learning and behavior in Procambarus clarkii (red swamp crayfish), a sensitive bioindicator species. Crayfish were placed in an aquatic Tmaze (classic method to test cognitive ability) with a food reward in a side arm. Various behavioral endpoints were recorded over repeated trials, including time to reward, time to reward arm, percent of crayfish to not locate reward arm, time spent in the under cover area, and time needed to complete ~180° turnarounds. Concentrations of the chemicals tested represented an environmentally realistic range. Each treatment level of atrazine, DEA, DIA and HA resulted in significant deficits compared to control for at least two behavioral endpoints. Furthermore, a nonmonotonic dose-response was observed for atrazine. Based on these results, crayfish exposed to atrazine and each degradate at low, biologically relevant doses had impaired boldness and explorative behavior compared to control. Thus, crayfish exposed to these contaminants in natural environments will have impaired abilities to locate food, find mates, and avoid predation, which will have a profound impact on their ability to survive. These implications extend beyond crayfish, a keystone species, to include any species that rely on them as a food source or as a source of vital energy to the ecosystem via their roles as detritus shredders