Sean Comber

Inputs, Monitoring and Fate Modelling of Antifouling Biocides in UK Estuaries

Abstract The use of antifouling paints containing tributyltin as a biocide is now limited to vessels greater than 25 m in length. Consequently, manufacturers have introduced additional biocides which are generally used in combination with copper. These biocides are termed booster biocides, and currently there are nine approved for use on leisure craft. The environmental impact of tribuyltin and copper on the environment is well documented. However the potential for the other biocides to cause pollution has not been quantified. A survey was therefore performed to determine the quantity of each of the biocides released to coastal waters. Copper(I) oxide was used in highest quantities followed by diuron, copper thiocyanate, Irgarol 1051, zinc pyrithione and dichlofluanid. Monitoring studies agreed with the survey, concentrations of copper being highest followed by diuron and irgarol. High concentrations of zinc were also observed, probably arising from sacrificial anodes. Generally, predictions of biocide concentrations, obtained using an existing exposure model, were similar to measured concentrations, indicating that this model is a useful screening tool for risk assessment purposes.

Comparison of the partitioning of trace metals in the humber and Mersey Estuaries

Abstract Studies into the partitioning of trace metals between the dissolved phase and suspended solids have been performed on two major UK estuaries, the Mersey and the Humber. Aqueous phase trace metal concentrations were determined, along with partitioning data ( K p ) determined from both laboratory equilibration experiments and by chemical leaching techniques. Dissolved trace metals in the Humber essentially exhibited conservative behaviour (or a slight positive deviation). In the Mersey, however, removal of zinc, chromium, and, in particular, copper and cadmium occurred in the low salinity region. Sequential extraction data gave an indication of the nature of trace metal bindings to suspended sediment, and revealed total extractable trace metals on the Mersey suspended sediment to be a factor of two greater than that found in the Humber. Similarly, partition coefficients in the Mersey were approximately an order of magnitude greater than in the Humber. Chloro-complexation was shown to control the partitioning of cadmium within estuaries. Copper, however, exhibited a distinct trend of increasing K p with increasing salinity.

Abiotic persistence of atrazine and simazine in water

Hydrolysis and photolysis experiments have been undertaken to investigate the abiotic persistence of atrazine and simazine in a variety of waters. Hydrolysis only occurs to a significant extent at pH values at the lower limit of those found in the natural aquatic environment (pH 4.0 or less). Photolysis was initiated by a wide range of wavelengths in waters at pH 4.0, but only by more energetic wavelengths of less than 300 nm at higher pH values (pH 6 to 8). Based on these data, the aquatic half-life of atrazine and simazine in well-lit acidic upland waters will be typically six days. In lowland rivers with higher pH (7 to 8.5), these triazines are likely to exhibit half-lives of months rather than days. In groundwaters, atrazine and simazine will have half-lives in the order of years, due to the exceedingly slow rate of hydrolysis. © 1999 Society of Chemical Industry

Performance of UK wastewater treatment works with respect to trace contaminants

This study examined the performance of 16 wastewater treatment works to provide an overview of trace substance removal in relation to meeting the objectives of the Water Framework Directive (WFD). Collection and analysis of over 2400 samples including sewage influent, process samples at different stages in the treatment process and final effluent has provided data on the performance of current wastewater treatment processes and made it possible to evaluate the need for improved effluent quality. Results for 55 substances, including metals, industrial chemicals and pharmaceuticals are reported. Data for sanitary parameters are also provided. A wide range of removal efficiencies was observed. Removal was not clearly related to the generic process type, indicating that other operational factors tend to be important. Nonetheless, removals for many substances of current concern were high. Despite this, current proposals for stringent water quality standards mean that further improvements in effluent quality are likely to be required.

Hydride-trapping techniques for the speciation of arsenic

The determination of arsenic species by the trapping of volatile hydrides prior to atomization in the light path of an atomic absorption spectrometer is described and its operation in the measurement of arsenic species in the marine environment are discussed. Examples are drawn from the analysis of Tamar estuary water and sediment interstitial (pore) waters and from studies of the temporal variation of dimethylarsenic in coastal waters. Improvements in both the design and operation of the technique have resulted in enhanced performance. Baseline resolution of inorganic arsenic, monomethylarsenic and dimethylarsenic is now possible and trimethylarsine is resolved. Ultraviolet photolysis of arsenobetaine and arsenocholine gives partial conversion to trimethylarsine oxide. This can be employed in the qualitative appraisal of the presence of trimethylarsenic species. Current detection limits (3 sigma) for inorganic, mono- and di-methylarsenic lie in the range 19 to 61 pg absolute, giving 19–61 ng/1 concentration detection limits for 1 ml samples. This can be improved even further by using larger sample volumes. The properties of the analysis system when presented with various arsenic species are described. A ca. 10% loss of arsenite occurs in samples stored at —20 °C and immediate freezing of samples in liquid nitrogen is recommended.

Which offers more scope to suppress river phytoplankton blooms: Reducing nutrient pollution or riparian shading?

River flow and quality data, including chlorophyll-a as a surrogate for river phytoplankton biomass, were collated for the River Ouse catchment in NE England, which according to established criteria is a largely unpolluted network. Against these data, a daily river quality model (QUESTOR) was setup and successfully tested. Following a review, a river quality classification scheme based on phytoplankton biomass was proposed. Based on climate change predictions the model indicated that a shift from present day oligotrophic/mesotrophic conditions to a mesotrophic/eutrophic system could occur by 2080. Management options were evaluated to mitigate against this predicted decline in quality. Reducing nutrient pollution was found to be less effective at suppressing phytoplankton growth than the less costly option of establishing riparian shading. In the Swale tributary, ongoing efforts to reduce phosphorus loads in sewage treatment works will only reduce peak (95th percentile) phytoplankton by 11%, whereas a reduction of 44% is possible if riparian tree cover is also implemented. Likewise, in the Ure, whilst reducing nitrate loads by curtailing agriculture in the headwaters may bring about a 10% reduction, riparian shading would instead reduce levels by 47%. Such modelling studies are somewhat limited by insufficient field data but offer a potentially very valuable tool to assess the most cost-effective methods of tackling effects of eutrophication.

Partitioning of marine antifoulants in the marine environment

The partitioning behaviour of the organic biocides, Irgarol 1051 and diuron and two inorganic biocides (copper and zinc) was investigated using six sediments of differing physico-chemical properties collected from unimpacted sites along the south coast of England. The kinetics of sorption and equilibrium partitioning between the sediments and seawater were investigated over a period of 20 days. Resulting organic carbon/water partition coefficients (log Koc) were related to suspended sediment concentration and ranged from 2.28 to 5.20 for diuron; and from 2.41 to 4.89 for Irgarol 1051. Sediment/water partition coefficients (log Kp) for copper and zinc varied from 2.46 to 5.08 l/kg and from 2.49 to 4.97 l/kg, respectively. Kinetic data indicated that there were significant interactions between the dissolved and particulate phases at the start of the experiments, just after mixing. This is thought to be a result of redistribution of organic carbon between the two phases.

Determination of trace concentrations of hexavalent chromium

A simple and sensitive solvent extraction-atomic spectrometric technique has been developed for the determination of hexavalent chromium in fresh and saline waters. The technique is based on the reaction of chromium with diphenylcarbazide. The method has been tested on a variety of water samples over an analytical range of 0-2 microg l(-1). A limit of detection of 0.024 microg l(-1) was achieved. Spiking recoveries in the range 87-115% were achieved in river water, drinking water and marine waters.

Ecological risk assessment of contaminated soil

Abstract The basis for an ecological risk assessment based on meeting the needs of recent UK and EU legislation is described. The background to the framework and the legislative driver and relevant definitions of harm are provided, prior to an overview of the proposed ecological risk assessment process, which has been broken down into a Tiered approach. Tier 0 requires the establishment of a conceptual site model, where potential contaminant-pathway-receptor linkages are sought and, assuming they are identified, lead on to higher Tier assessments. Tier I relies largely on chemical analysis of soil contaminant levels and comparison with soil quality guideline values to assess the likelihood of harm. In some cases biological screening assays may also be undertaken within this Tier. Based on a weight of evidence approach, should data from Tier 1 indicate harm or leave uncertainty, then Tier 2 biological testing is undertaken using assays relevant to the site of interest. In situations where harm is identified under Tier 2 then Tier 3 is reserved for establishing the extent of harm within the ecosystem. Finally the use of the ‘weight-of-evidence’ approach to generate scientifically robust conclusions regarding the harm (or potential for harm) within the ecosystem is briefly outlined. The framework discussed is currently being adopted by the UK Environment Agency, with implementation expected in 2005. The UK scheme compares favourably with comparative schemes operating in other countries possessing the merits of being iterative, tiered, flexible with agreed exit points subject to satisfying defined criteria and so speeding the decision-making process.

Survey of four marine antifoulant constituents (copper, zinc, diuron and Irgarol 1051) in two UK estuaries

A field survey of antifoulant concentrations was undertaken in two UK estuaries (Hamble and Orwell) in 1998 and 1999. The two locations offered variations in physical aspects (Orwell estuary being significantly larger than the Hamble) as well as differences in boat densities (Hamble having almost twice as many vessels moored in the estuary and marinas). Samples were analysed for copper, zinc, diuron and Irgarol 1051, and were collected in summer and winter in order to identify potential seasonal variations in concentrations. The effect that different marina types (e.g. locked marina, one located in a natural inlet and pontooned ones in the open estuary) had on antifoulant concentrations were also investigated. Concentrations of the organic booster biocides, diuron and Irgarol 1051 in the marinas and estuaries were mainly influenced by leaching from antifoulant paints applied to the hulls of leisure craft, and so levels reflected the number of vessels present in the water. As a consequence significantly higher concentrations were found in marinas (up to ca. 900 ng l(-1) for diuron and 240 ng l(-1) for Irgarol 1051) compared with estuaries (up to ca. 400 ng l(-1) for diuron and 100 ng l(-1) for Irgarol 1051) and in summer compared with winter. Sediment concentrations of Irgarol 1051 and diuron were rarely detectable other than in the marinas where high concentrations were detected near slipways assumed to be derived from washed off paint chips. Dissolved concentration profiles for copper and zinc in the estuaries and marinas were different from those for the organic booster biocides partly because other sources of these metals contributed to estuarine and marina loads. In particular, riverine loads and inputs from sacrificial anodes attached to leisure craft, exhibited a major influence of estuarine levels of zinc. Consequently, only in the Hamble estuary for copper was there a clear distinction between summer (typically 3-4 microg l(-1)) and winter dissolved values (typically 1-2 microg l(-1)) that could be largely attributable to the leaching of antifoulant paints. Sediment concentrations for both metals were similar for both estuaries, with little variation between winter and summer values (Zn ranging from 28 to 614 mg kg(-1) and Cu from 6 to 1016 mg kg(-1)) as with the organic booster biocides highest levels were measured at the base of slipways in marinas.