Recovery simulations of grossly polluted sediments in the Bilbao Estuary

Assessing the improvement of the Bilbao estuary water quality in response to pollution abatement measures

To evaluate the success of almost 20 years of pollution abatement in the Bilbao estuary watershed in northern Spain, we analyzed temporal trends in pollution discharges and water quality from 1993 to 2003. Over that period a great portion of the raw wastewater discharge was intercepted and treated, leading to a significant reduction in the pollution load to the estuary (51.8% in biochemical oxygen demand, 70.9% in ammonia nitrogen and 81.9% in faecal coliforms). Temporal trends of mean annual levels of water quality variables showed statistically significant increases in dissolved oxygen saturation (between 2.04 and 4.11%/year) and decreases in ammonia nitrogen (between -4.15 and -175.75 microM NH3/year) and faecal coliforms concentrations (from 2.55 x 10(5) to 2.13 x 10(4) CFU/100ml). The improvement of the Bilbao estuary water quality reported in this paper is primarily attributed to the pollution abatement measures accomplished by the local water authority. Finally, as a result of these pollution control efforts, European bathing water quality standards were met at local beaches.

Heavy-metal and microbial depuration of the clam Ruditapes decussatus and its effect on bivalve behavior and physiology

The bivalve Ruditapes decussatus was evaluated as a possible biomonitor of heavy-metal contamination. Concentrations of copper (Cu), cobalt (Co), iron (Fe), nickel (Ni), and manganese (Mn) were measured in R. decussatus. Water and sediment samples were collected at two stations of Timsah Lake in Ismailia, Egypt, from October to November 2002, using atomic absorption spectrophotometry (AAS). Results from the heavy-metal and microbial analyses indicated that site II was less contaminated than site I. The bivalve showed accumulation of metals, with a bioaccumulation factor (BAF) greater than 4. The bioaccumulation of metals varied strongly according to the sampling site. After 48 h of depuration, Fe, Ni, Co, Cu, and Mn were reduced significantly, to 46.8% and 47.7%, 19.9% and 20.3%, 27.3% and 27.9%, 35.9% and 36.6%, and 18.2% and 26.6%, compared with the initial concentrations, in clam tissue at the two stations. In bivalves from site II the counts of total bacteria, fecal coliforms, and bacterial pathogens were reduced by more than 90%, whereas phage counts were only reduced by 56% after 4 days of depuration. The depuration of bivalves collected from the heavily polluted site (I) was not effective, as coliforms were reduced only by 85% after 4 days, whereas counts of pathogens and pathogenic indicators such as Vibrio, fecal Streptococcus, and coliphage decreased to less than 50% of the initial concentration. The time necessary to decrease contamination to 10%, 50%, and 90% for clams at both stations was consistently shorter for heavy metals than for microorganisms. Investigation of the effects of heavy-metal and microbiological depuration on valve movement and physiological rates (oxygen consumption and ammonia excretion) was carried out on R. decussatus to test the utility of physiological stress indices in assessing the health of depurated animals. Clams in the experimental tanks exhibited various states of activity, which were rated by identifying and scoring (0-4) the different parameters, including shell gap, siphon extension, and foot protrusion. Moreover, an increase in ammonia excretion was usually associated with an increase in respiration rate. The oxygen-to-nitrogen ratio provided a sensitive indicator of bivalve health. It can be concluded that shellfish monitoring and depuration data depended on the initial concentration of the pollutants. There were differences in the physiological responses of clams from the two sites during the periods of pre- and postdepuration of the contaminants. There was a significant correlation between reduction of metal concentration in clam tissue and enhancement of valve movement, as well as activity and increasing respiration rate.