| Abstract
| - Measurements of simultaneously extracted metals (SEM),acid volatile sulfide (AVS), and invertebrate toxicitywere combined with X-ray absorption spectroscopy (XAS)to evaluate metal speciation and ecological hazard ofcontaminated sediments from the Seaplane Lagoon, NavalAir Station Alameda (CA). This site is characterized bymoderate to low toxicity in surface sediments and by metalconcentrations in sediments and porewaters that increasewith depth. Standard 1-h ΣSEM/AVS measurements forsurface sediments were compared with time-series (0.25−24 h) measurements of metal and sulfide release fromsediments at 30 cm. Results show that AVS is rapidly andcompletely evolved after 1 h, but metal extractioncontinues with time and is not complete after 24 h. Sediment−water interface tests of invertebrate toxicity using sanddollar embryos (D. excentricus) and adult amphipods (E.estuarius) exposed to intact cores showed no to low toxicityin surface sediments. In sediments from 30- and 60-cmdepth, high toxicity in several replicates was attributed tofactors other than metal concentrations, such as highdissolved ammonia or low dissolved oxygen concentrations.Metal speciation and bonding determined from XASshow that cadmium (100%), zinc (≈80%), and manganese(≈50−70%) are associated with monosulfide phases inthe sediments. The remaining fraction of zinc and manganeseand all of the chromium and lead are ligated by oxygenatoms, indicating association with oxide, carbonate, or silicateminerals. Iron is present in the sediments in two fractions,as Fe(II) in the sulfide phase pyrite and as oxygen-ligated octahedral iron, probably associated with clayminerals. Bulk chemical measurements of porewaters andsediments, and speciation information from XAS, suggestthat AVS could be accounted for by volatilization of porewatersulfide. Our results indicate that metals are removedfrom porewaters by formation of monosulfide phases onlyfor cadmium and partially for zinc and manganese butnot for lead or chromium, even though these are reduced,anoxic sediments typical of a restricted marine estuaryenvironment. Comparison of geochemical, spectroscopic,and biological data provides new insight for the interpretationof ΣSEM/AVS measurements and points out the need forsynergistic biological/geochemical tests for determiningpotential ecological hazard.
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