Seasonal changes in mineralization of xenobiotics by stream microbial communities

Abstract

Seasonal changes in the mineralization of mixed amino acids (MAA), an anionic surfactant (linear alkylbenzene sulfonate; LAS), a detergent builder (nitrilotriacetic acid; NTA), and a herbicide (2,4-dichlorophenoxyacetic acid; 2,4-D) by microbial communities were studied in two streams in southwestern Ohio. Radiolabeled (14C) test compounds were added to samples of seston, leaf litter, periphyton, and sediment collected from Briarly Creek, a waste water impacted stream, and Little Indian Creek, a relatively unimpacted stream. Mean values for NH3, orthophosphate, dissolved organic carbon, and total organic nitrogen were significantly higher in Briarly Creek than Little Indian Creek. However, there was no significant difference in the mean values for esterase activity, chlorophyll a, and bacterial numbers in the respective habitats of the two streams. Mineralization was a significant method for removal of MAA, LAS, and NTA in Briarly Creek, and MAA in Little Indian Creek throughout the year. Mineralization of 2,4-D by microbial communities in both streams was very limited. The importance of temperature as an environmental variable affecting mineralization was indicated by (i) lower first-order rate constants in winter samples as compared with summer samples in some habitats; (ii) an increase in the first-order rate constants when temperatures were increased from 4 to 22 °C; and (iii) a positive correlation of LAS mineralization with ambient temperature. Key words: streams, xenobiotics, biodegradation, leaf litter, seston, periphyton, sediments.