Fate of the nonsteroidal anti-inflammatory drug naproxen in agricultural soil receiving liquid municipal biosolids

Abstract

Naproxen (2-(6-methoxy-2-naphthyl) propionic acid) is widely used for the treatment of pain and swelling associated with arthritis, gout, and other inflammatory conditions. Naproxen has been detected in municipal sewage outflows and in surface waters and could reach agricultural land through the application of municipal biosolids or reclaimed water. The persistence characteristics of naproxen in three agricultural soils were investigated. In laboratory microcosms of moist soil incubated at 30 degrees C, [O-14CH3]naproxen was rapidly and thoroughly mineralized to 14CO2 with comparable kinetics in a sandy loam soil, a loam soil, and a silt loam soil. Naproxen mineralization was responsive to soil temperature and soil moisture content, consistent with the primary mechanism of dissipation being biodegradation. Mineralization of naproxen was hastened by the addition of liquid municipal biosolids (LMBs) from a municipal sewage treatment plant that aerated this material. Naproxen was stable in autoclaved soils with or without addition of autoclaved LMBs, whereas naproxen was rapidly mineralized in sterile soil supplemented with nonsterile LMBs. An enrichment culture was obtained from aerobically digested LMBs in a mineral salts medium with naproxen as the sole source of carbon. The culture converted the parent compound to the corresponding naphthol, O-desmethyl naproxen. In summary, naproxen was rapidly removed from soil, with mesophilic aerobic biodegradation being the primary mechanism of dissipation. Microorganisms carried in biosolids enhanced naproxen dissipation in soil, with the initial mechanism of attack likely being O-demethylation. We conclude on this basis that naproxen in soils receiving biosolids would be readily biodegradable and, in the absence of preferential flow or runoff, pose little risk for contamination of adjacent water or crops.