|Thurman, E - USGS|
|Blanchard, Paul - U OF MO|
Submitted to: Journal of Society of Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 8, 1999
Publication Date: N/A
Interpretive Summary: Atrazine is the major herbicide used for weed control in corn. In soils, atrazine degrades to several different compounds, with hydroxyatrazine (HA) often the major break down product. HA has been shown to contaminate streams throughout the Corn Belt, and its pattern of contamination suggests that it persists in soils and may be present in stream sediments. However, ,no one has ever measured the amounts of HA in soils or stream sediments. This study was conducted to determine the amounts of HA in four soils with varying atrazine use histories and in stream sediments from a creek in a predominantly agricultural watershed in north-central Missouri. The results of the study showed that significant amounts of HA were found in all soils, even 3 years after atrazine had been applied. HA was always found at greater levels than atrazine and two of its other break down products. HA was also found in stream sediments at higher levels than atrazine. From this study and others on HA, we know that one of the important transport pathways causing HA contamination in streams is by the following sequence: farmers apply atrazine to soils; atrazine breaks down to HA; erosion deposits soil containing HA into streams; flowing stream water washes HA off the stream sediments; HA contamination of stream water occurs year-round. Is HA toxic to humans or animals? We know that heavy doses of HA do not cause cancer in laboratory animals, but we do not know if chronic low level exposure may have long-term negative impacts on human health or on stream ecosystems. Results from this study will benefit scientists and regulatory personnel by helping them understand the transport and fate of HA in the environment. Therefore, they will be better able to assess health risks associated with long-term HA exposure.
Technical Abstract: Knowledge of hydroxyatrazine (HA) sorption to soils, and its pattern of stream water contamination suggest that it is persistent in the environment. Soils with different atrazine use histories were collected from four sites, and sediments were collected from an agricultural watershed. Samples were exhaustively extracted with a mixed-mode extractant, and HA was quantitated using HPLC with UV detection. Atrazine deethylatrazine (DEA), and deisopropylatrazine (DIA) were also measured in all samples. HA concentrations were considerably greater than atrazine, DEA, and DIA in all soils and sediments studied. HA soil concentrations ranged from 14 to 640 ug/kg with a median concentration of 78 ug/kg. HA sediment concentrations ranged from 11 to 96 ug/kg with a median concentration of 14 ug/kg. Correlations of HA and atrazine concentrations to soil properties indicated that HA levels in soils were controlled by sorption of atrazine. Since atrazine hydrolysis is known to be enhanced b sorption and pH extremes, soils with high organic matter and clay content and low pH will result in greater atrazine sorption and subsequent hydrolysis. Significant correlation of HA concentrations to organic matter, pH, and cation exchange capacity of sediments indicated that mixed mode sorption (i.e., binding by cation exchange and hydrophobic interactions) was the mechanism controlling HA levels in sediment. The presence of HA in soils and stream sediments at the levels observed support existing hypotheses regarding its transport in surface runoff. These results also indicated that an additional risk factor associated with atrazine usage is the potential impact of sediment-bound HA on aquatic ecosystems.