The success of elutriate tests in extended prediction of water quality after a dredging operation under freshwater and saline conditions.

Dredging simulation by elutriate tests accurately predicted concentrations of Hg, Cu, Mn and Fe released to the water column from contaminated sediment to within 1 order of magnitude. Hg and Cu concentrations increased by up to 7-fold after dredging, but declined to background concentrations within 48 h. Maximum loadings of Hg and Cu coincided with Fe and total organic carbon (TOC) water column concentrations, suggesting Hg and Cu are adsorbed onto particulates of Fe oxides and organic material. Seasonal changes in redox potential and temperature did not significantly affect metal release from sediments. Saline water did not cause significant increases in contaminant release from sediments to the water column over that observed for freshwater. Water quality standards of 1 µg l(-1) Hg and 28 µg l(-1) Cu as annual averages were not breached by dredging operations. Long-term effects of dredging on Hg and Cu availability, due to deposition of contaminated material as surficial sediments, is, however, of concern.

Depositional profiles and relationships between organotin compounds in freshwater and estuarine sediment cores.

A range of organotin compounds including tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) were measured in sediment cores collected from contaminated freshwater and estuarine sites in Essex and Suffolk, U.K. Butyltin compounds were found in significant quantities at depths of up to 60 cm within the sediments of marina and boatyard complexes with TBT concentrations ranging from <3 ng g(-1) (the detection limit) to >3000 ng g(-1). In general sediment TBT concentrations decreased with depth, but maximum enrichment tended to occur just below the surface. It was evident from these core profiles that the accumulation of organotins in surface deposits was on the decline and coincided approximately, with the implementation in 1987 of the UK retail ban on the sale of TBT based antifouling paints for application on vessels <25 m in length. The degradation rate for TBT in sediments was found to exhibit first order kinetics with half lives ranging from 0.9-5.2 years between different sites. Estimated degradation rates have also been determined for DBT and MBT. These ranged from 1.5-3.0 years for DBT and 1.8-3.7 years for MBT.

Spatial distribution of organotins in sediments of lowland river catchments.

A method is described for the measurement of nanogram quantities of a range of methyl and butyltin compounds. The method utilises a modified purge and trap/boiling point separation technique for the determination of organotin compounds in sediment samples. A spatial survey of sediment samples within 5 river systems in the East Anglia region of the United Kingdom was undertaken and identified a range of organotin compounds with concentrations of tributyltin (TBT) ranging from <3.9 ng g(-1) up to 1291 ng g(-1). The highest values were found in areas connected with boating activities. Wherever TBT was present, dibutyltin and monobutyltin were most commonly found along with small concentrations of certain methyltins.

The impact of heavy metals on lowland rivers and the implications for man and the environment.

Increased public awareness of river water quality problems has led to concern over the continued discharge of low-level contaminants in sewage treatment work (STW) final effluents. This paper discusses the source and nature of heavy metals during sewage treatment processes and examines their behaviour and fate in the aquatic environment. The influences of physico-chemical parameters and chemical speciation on metal mobility during sewage treatment and in receiving waters have been assessed. The importance of metal speciation with regard to aquatic toxicology is discussed and the effectiveness of current legislation in controlling the release of heavy metals to lowland river systems has been reviewed.