Linkage of bioaccumulation and biological effects to changes in pollutant loads in south San Francisco Bay

The developed world has invested billions of dollars in waste treatment sin ce the 1970s; however, changes in ecological or biological responses are ra rely associated with reductions in metal pollutants. Here we present a nove l, 23-yr time series of environmental change from a San Francisco Bay mudfl at located 1 km from the discharge of a suburban domestic sewage treatment plant. Samples of surface sediment, the bioindicator Macoma balthica, and m etals loading data were used to establish links between discharge, bioaccum ulation, and effects. Mean annual Ag concentrations in M. balthica were 106 mu g/g in 1978 and 3.67 mu g/g in 1998. Concentrations of Cu declined from 287 mu g/g in 1980 to a minimum of 24 mu g/g in 1991. Declining; Cu bioacc umulation was strongly correlated with decreasing Cu loads from the plant b etween 1977 and 1998. Relationships with bioaccumulation and total annual p recipitation suggested that inputs from nonpoint sources were most importan t in controlling Zn bioavailability during the same period. Ecoepidemiologi cal criteria were used to associate failed gamete production in M balthica to a metals-enriched environment. Reproduction persistently failed between the mid-1970s and mid-1980s; it recovered after metal contamination decline d. Other potential environmental causes such as food availability, sediment chemistry, or seasonal salinity fluctuations were not related to the timin g of the change in reproductive capability. The results establish an associ ative link, suggesting that it is important to further investigate the chem ical interference of Cu and/or Ag with invertebrate reproduction at relativ ely moderate levels of environmental contamination.