Metals sediment toxicity: Chemical approach by SEM/AVS ratio. Application on Seine estuary sediments

Abstract

Within the framework of environmental quality criteria for certain heavy metals in sediment, Acid Volatile Sulphides (AVS) has been proposed as the primary standardisation parameter in combination with the amount of simultaneously extracted metals (SEM). AVS, comprising essentially iron monosulphides in sediments, are available for binding divalent cationic metals through the formation of insoluble metal-sulphide complexes, thereby controlling the metal bioavailability and subsequent toxicity for benthic biocommunities. AVS is operationally defined as the amount of sulphides that can be volatilised during a cold acid extraction. The AVS-bound metals, with environmental concern (usually Cd, Cu, Ni, Pb and Zn), are extracted at the same time and are called simultaneously extracted metals (SEM). The ratio or the difference between AVS and SEM gives an indication of the potential sediment toxicity. Such problems on extraction procedure appears: for AVS hydrochloric acid 6 mol/dm 3 is currently used even so for SEM use of hydrochloric acid 1 mol/dm 3 is advised. To investigate the influence of acid strength, sulphides and metals extractions are realized on anoxic sediments from seine estuary. SEM/AVS ratio for different acid was calculated and toxicity associated is discussed.