MEASUREMENT AND DISTRIBUTION OF INTERSTITIAL AND OVERLYING WATER AMMONIA AND HYDROGEN-SULFIDE IN SEDIMENT TOXICITY TESTS

Hydrogen sulfide and ammonia are naturally occurring and anthropogenic ally enriched components of marine sediments which may occur in concen trations toxic to marine organisms. In this study, ammonia and hydroge n sulfide were measured in interstitial and overlying water at the ini tiation and termination of solid phase toxicity tests using amphipods (Rhepoxynius abronius). Interstitial hydrogen sulfide concentrations w ere generally higher than overlying concentrations, presumably because hydrogen sulfide that diffused from sediments was quickly volatilized in the overlying water. Unionized ammonia concentrations were higher in interstitial water at test initiation, but were often higher in ove rlying wafer after 10 day exposures. The pH was higher in overlying wa ter samples than in interstitial samples, and contributed to increased proportions of unionized ammonia in the overlying water. Concentratio ns of hydrogen sulfide and ammonia above the effects threshold for Rhe poxynius occurred more predominantly in the interstitial water. Eight of twelve treatments with high hydrogen sulfide concentrations, and fi ve of eight treatments with high ammonia concentrations, had significa nt toxicity. Based on these results we suggest measuring initial and f inal interstitial concentrations of hydrogen sulfide and ammonia, and initial and final concentrations of overlying ammonia. A precise metho d of sulfide measurement in seawater is presented, bared on techniques and equations from the literature. (C) 1997 Elsevier Science Ltd.