Distribution of atrazine into three chemical fractions: impact of sediment depth and organic carbon content

The fate and transport of organic contaminants in aquatic sediments are impacted largely by microbial degradation and sorption to organic matter. Atrazine, a pre-emergent herbicide, has the potential to contaminate groundwater because of its slight water solubility, long half-life, and sorption to organic matter. Mineralization and distribution of 14C-atrazine into three chemical fractions were monitored over time in surface and subsurface coastal aquatic sediments of different land use. Sediments were extracted with an organic solvent followed by an alkali hydrolysis, and 14C activity was measured in the aqueous, solvent, and basic fractions (representing nonsorbed compounds, loosely sorbed compounds, and humic or fulvic acid bound compounds, respectively). Limited mineralization of atrazine occurred (< 4%). The 14C activity in the aqueous and basic fractions increased over time, was greater in surface versus subsurface sediments, and was positively correlated with sediment organic carbon (SOC) content, indicating greater biological and chemical activity. Total 14C recovered ranged from 50 to 90%, was less in surface versus subsurface sediments, and was not correlated with SOC after 80 d. These results suggest that in native aquatic surface sediments, atrazine sorption plays a major role, whereas in subsurface sediments atrazine may be available for degradation and transport to shallow groundwater.