It is well established that chlorination in water treatment produces numerous organic disinfection by-products (DBPs) with potential adverse health impacts. Naturally occurring humic substances serve as the major precursors for the reaction with chlorine to produce a variety of DBPs, including well identified trihalomethanes (THM), haloacetic acids (HAA), etc. Overshadowed by the reported toxicity in drinking water, DBPs have never been studied for their potentials as pesticides, albeit the fact that more than half of the top 25 most commonly used pesticides are organohalogens. The majority of DBPs remain unidentified due to the heterogeneous nature of humic substances. Thus, unlike synthetic pesticides with well-defined structures, the majority of DBPs (if could function as pesticides) are mixtures of complex organohalogens with no fixed compositions. Therefore, they have no specific targets that insects can develop resistance to, as they do to synthetic pesticides. Our exploratory study was carried out using well-characterized reference material: Suwannee River, Pahokee peat, Elliott soil, and Leonardite humic acid standards (all from International Humic Substance Society) as well as Lipton instant tea powder. DBP formation potential experiments at chlorine to total organic carbon ratio of 2.5 at pH 7 and 8.5 for a contact time of 24 hours at 25°C showed chlorine demand and formation of THM and HAA at similar levels for all the studied humic substances and instant tea. Additional mass spectrometric and spectroscopic analyses of other DBPs are currently underway. Brine shrimp lethality bioassay will be used to test the cytotoxicity of DBPs and compared to chloropicrin, the ninth commonly used pesticide and also a DBP. As a footnote, Grace Wu is currently a junior in high school. Wells Wu (Grace Wu’s father) did DBP research during 1991-2001. Wells taught Grace the formation and presence of DBPs in tap water. Grace conceived the idea of using DBPs as potentially safer pesticides and is drawn to the possible benefits to our ecology.

Disinfection by-products as green pesticides?

256th National Meeting (2018)

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