The biodegradation of linear alkylbenzene sulfonate (LAS) and nitrilotriacetic acid (NTA) was assessed in an established septic tank system and an adjoining shallow sand aquifer (located near Cambridge, Ontario). Studies were conducted on soil, aquifer sediment, and groundwater samples from a transect of the septic tank effluent plume. LAS and NTA were readily biodegraded in the vicinity of the discharge, with mineralization half‐lives in soil and sediment samples collected near the tile field ranging from 9 to 17 d and 1 to 3 d, respectively. Similar results were obtained for ground water. Adaptation was a key process in the system, as illustrated by the rapid biodegradation near the tile field and limited biodegradation at locations far downgradient or ungradient of the system, where little or no LAS or NTA loading occurred. The results demonstrate that properly functioning septic tank systems can effectively remove synthetic organic chemicals such as LAS and NTA.

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