The potential risks and bioavailability of herbicides to non-target aquatic plant communities depends on various factors, including chemical properties and environmental factors. Such environmental factors include the dissolved / particulate organic carbon present. Atrazine, a terrestrial herbicide that is commonly detected in aquatic environments, will be tested at five different concentrations with varying levels of dissolved organic carbon, as well as with no natural organic matter (NOM) in the aquatic plant species lemna minor (duckweed).  This will be done with a 5×5 factorial study in the lab to evaluate how dissolved organic matter with influence the bioavailability of atrazine in duckweed. This project will provide insight into how natural organic matter influences toxicity of atrazine. Results will also be useful for characterizing how protective water quality criteria based on lab tests are relative to real-would conditions.