PubMed Health⌕ Search

Biomedical subjects

M D Scrimshaw

Publications and source records attributed to M D Scrimshaw.

16 recordsLinked to original sources
PubMed2005

Butyltin compounds in a sediment core from the old Tilbury basin, London, UK.

Sections from a sediment core taken from the River Thames were analysed for butyltin species using gas chromatography with species-specific isotope dilution mass spectrometry. Results demonstrated that in most samples tributyltin concentrations of 20-60 ng/g accounted for <10% of the total butyltin species present, which is in agreement with data from other sediment samples which were historically contaminated with tributyltin. Vertical distribution of the organotin residues with depth throughout the core, with data on organochlorine compounds and heavy metals allowed for the construction of a consistent hypothesis on historical deposition of contaminated sediments. From this it was possible to infer that the concentrations of tributyltin in sediments deposited during the early 1960s were in the order of 400-600 microg/g by using degradation rate constants derived by other workers. Such values fall well within the range quoted for harbour sediments in the literature.

Environmental Monitoring↗
PubMed2004

Removal of organotins during sewage treatment: a case study.

Discharge consents for tributyltin (TBT) from wastewater treatment works in the UK are set by the Environment Agency. These values are normally derived from the Environmental Quality Standards for concentrations of TBT in the receiving water, based on the volume of effluent discharged and subsequent dilution within the environment. In this study, a sampling program was designed to monitor concentrations of TBT (and other organotins) in the influent and effluent at each stage of treatment. Sampling was undertaken at 3 hourly intervals, over 24 hours, at 8 locations throughout the works for five days. Organotin concentrations were determined using capillary gas chromatography with flame photometric detection. The results demonstrated that TBT was consistently present in the influent at concentrations of approximately 0.1 microg l(-1). However, a "pulse" of TBT and monobutyltin (MBT) was observed on the third day when the concentration of TBT and MBT in the influent increased to 14 microg l(-1). This "pulse" of TBT and MBT was also observed as the wastewater passed through the unit treatment processes. Concentrations of both compounds were much reduced in the final effluent (TBT 2.5 microg l(-1) and MBT 6.9 microg l(-1)). Over the entire period, the average removal of TBT during primary treatment was 81%, and during secondary biological treatment was 71%. The overall removal efficiency of the plant, taking into account the recycling of returned liquors was 86% between influent and effluent for TBT. Removal efficiency of TBT was correlated to that of suspended solids, and it was demonstrated that on days when suspended solids removal was low, TBT removal was also reduced. The mass flow of organotins through the plant indicated that the majority of TBT was concentrated into the sewage sludge. Concentrations of TBT in sludge at the plant were approximately 18 microg kg(-1) (dry weight).

Organotin Compounds↗
PubMed2004

Analytical methods for the determination of alkylphenolic surfactants and polybrominated diphenyl ethers in wastewaters and sewage sludges. I a review of methodologies.

Alkylphenolic surfactants (alkylphenol polyethoxylates) and the polybrominated diphenyl ether flame retardants are important environmental contaminants and have been implicated as endocrine disrupters. Both groups of compounds have come under increasing scrutiny from legislators and there are proposals to curb their use. However, these compounds continue to enter the environment and there is a need to determine their occurrence, fate and behaviour throughout the hydrosphere and in wastewater treatment processes to determine mass fluxes and sources. This paper reviews analytical methods for their determination in the aqueous and solid (sediment / sludge) phase. Extraction, cleanup and quantification by gas and liquid chromatographic (GC and LC) techniques linked to mass spectrometric (MS) detectors are considered. The literature indicates that for the alkylphenols research papers favour the use of LC/MS which is more amenable to determination of more highly ethoxylated oligomers, however, standard methods focus on GC/MS and the less ethoxylated oligomers and parent alkylphenols. The use of GC with negative chemical ionisation MS techniques predominates for the analysis of polybrominated diphenyl ethers.

Chemistry Techniques, Analytical↗
PubMed2004

Quantifying uncertainties in the assessment of sediment quality: statistical criteria and guidelines for sediment quality assessments.

Current sediment quality guidelines generally adopt a tiered approach in order to assess sediment quality more cost-effectively. The uncertainties involved in the tiered approach of an integrative assessment, however have not been quantified resulting in a risk of committing type I error or type II error at the final confirmatory stage. This study develops statistical criteria and guidelines for the sediment chemistry component of an integrative assessment of sediment quality. At the tier 1 screening stage, historical data or an initial survey is required to determine the minimum sample numbers that will be required to be representative of the study site. Understanding the guiding principles which have underpinned the setting of sediment quality criteria for contaminant is an important factor in tier 1 evaluations. To reduce cost and uncertainty in data, sampling should include the least number of samples necessary to minimise uncertainties by estimating the probability distribution function (which represents the variability of the natural environment at the location of concern), with subsequent application of kriging and sequential simulation methods on data obtained. Implementation of statistical criteria and guidelines in sediment quality assessments can provide a foundation for a further quantitative cost/benefit analysis and decrease the risk of committing type I and type II statistical errors at later classification stages.

Environmental Monitoring↗
PubMed2004

Analytical methods for the determination of alkylphenolic surfactants and polybrominated diphenyl ethers in wastewaters and sewage sludges. II method development.

Analytical methods for the determination of two groups of compounds, the non-polar alkyl phenols along with their more polar ethoxylates, and the hydrophobic polybrominated flame retardants in wastewater samples have been developed. The methods allow for determination of the analytes in both the aqueous and solid phases, which were separated by centrifugation and filtration. Extraction from the aqueous phase involved the use of SPE for the surfactants, however, liquid-liquid extraction was found to be more efficient for the PBDE. Alkyl phenols and their ethoxylates were extracted from the solid phase by shaking with solvent and Soxhlet was used for extraction of PBDE. Sample cleanup was based on alumina columns for the PBDE and surfactants when extracted form solids. Quantification of surfactants utilised LC-MS with ESI in both positive and negative ionisation mode, and GC-MS (NCI) was used to determine the PBDE, with the exception of the deca congener, where a 10 m column installed on GC-ECD resulted in short run times and reduced thermal decomposition. Method recoveries for the surfactants were above 80%, and for PBDE 92.5% from the solid phase and 95+/-5% from the liquid phase.

Chromatography, Liquid↗
PubMed2003

Public perceptions and attitudes towards an established managed realignment scheme: Orplands, Essex, UK.

Where appropriate, managed realignment is the preferred policy option for sustainable coastal defences in the UK, since it provides both economic and ecological advantages. Until recently however, research has failed to address the social implications of this policy option having only acknowledged that communities in general, show reluctance in conceding land to the sea. Orplands managed realignment scheme is the third in a series of case studies to address a variety of social issues, but with a particular focus on the public acceptance of schemes and public confidence in the Environment Agency. It is hypothesised that local residents will be more accepting of a realignment scheme the longer it is in the public domain, rather than at its inception or construction. This paper presents findings from the Orplands scheme and demonstrates that overall scheme acceptance was greater at this site in comparison to previous case studies. Despite this, respondents did not show any more confidence in the Environment Agency and this has been attributed to their general scepticism towards a statutory body and the lack of recent contact between the various stakeholders. It is suggested that the development of criteria for consultation and public participation would facilitate public acceptance of managed realignment schemes.

Adolescent↗
PubMed2002

Prediction of the bioaccumulation factors and body burden of natural and synthetic estrogens in aquatic organisms in the river systems.

This study undertakes an initial prediction of the bioaccumulation factors and body burden of the steroid estrogens, estrone, estradiol, estriol and ethinylestradiol in a range of aquatic organisms (plankton, benthic and free-living invertebrates and fish) in river systems using a food-web model. These data are compared to that derived from less complex predictions based on octanol-water partition coefficient and molecular connectivity index. The model predicted that bioaccumulation of steroid estrogens occurred in all organisms, however, the values were small, and the maximum and minimum bioaccumulation factors in this study were found in the fish at the lowest trophic level with ethinylestradiol (332) and the fish at the highest trophic level with estriol (1.8), respectively. Moreover, the bioaccumulation factors were sensitive to the metabolic rates of the estrogens in the free living organisms, while the concentration of estrogens in sediment was a significant factor in determining these values in benthic invertebrates. Biomagnification contributed little to the overall bioaccumulation, but the importance increased in fish exposed to ethinylestradiol. The predicted bioaccumulation factors from the food web model were generally smaller than the calculated bioconcentration factors from the simpler octanol-water partition coefficient/molecular connectivity index based estimates. Compared to literature measured data, the predicted values for fish were approximately 1000 times less than the values observed in laboratory tests, while for invertebrates, the modeled values were less than two orders of magnitude below laboratory results. However, the model predicted a similar bioconcentration factor for plankton in relation to experimental data for Chlorella vulgaris for estrone and estriol.

Animals↗
PubMed2002

Partitioning of selected antifouling biocides in the aquatic environment.

Following a ban on the use of tributyltin in antifouling products on small boats, a number of organic booster biocides have been utilised in conjunction with copper in antifouling paints as alternative treatments. The fate of organic compounds in the aquatic environment is closely linked to their partitioning between aqueous media and sediment. In this study, experiments were designed to investigate the partitioning and sorptive behaviour of Irgarol 1051, chlorothalonil, dichlofluanid and diuron in the aquatic environment. Factorial experiments were undertaken to determine the importance of pH, particulate matter concentration and salinity to their sorption. A Mackay fugacity model was also applied. Results demonstrated that dichlofluanid had the stronger adsorption characteristics and was predicted to bind more strongly to sediments than Irgarol or chlorothalonil. Diuron exhibited the least preference for sorptive behaviour. Sorption appeared to be enhanced by increased suspended matter, whilst salinity does not seem to play a significant role in the partitioning behaviour of these biocides.

Absorption↗
PubMed2002

The effects of natural and synthetic steroid estrogens in relation to their environmental occurrence.

Laboratory-based acute toxicity data and physiological studies relating to natural and synthetic steroid estrogens in a range of animals and plants are reviewed. Steroid estrogens may induce adverse effects in animals that do or do not express the estrogen receptor, and in plants, and they may mimic other hormones or induce nonestrogenic effects. Although the findings of such studies should be treated with caution when extrapolated to possible environmental effects, the available data indicate that a wide range of effects may be manifested in a diversity of species. The environmental occurrence of the compounds and possible environmental exposure routes are also reviewed and discussed in relation to the laboratory-based acute toxicity data. While there are likely to be difficulties in relating some of the observed laboratory data to possible environmental effects, studies undertaken on fish are directly relevant because exposure pathways and concentrations were related to those occurring in the environment. Effects that may occur in the environment are discussed in relation to their significance to the individual and at the species level.

Animals↗
PubMed2002

Biotransformation and bioconcentration of steroid estrogens by Chlorella vulgaris.

The biotransformation and bioconcentration of natural and synthetic steroid estrogens by Chlorella vulgaris were investigated by using batch-shaking experiments with incubation for 48 h in the light or dark. Estradiol and estrone were interconvertible in both light and dark conditions; however, this biotransformation showed a preference for estrone. In the light, 50% estradiol was further metabolized to an unknown product. Apart from biotransformation, estrone, as well as hydroxyestrone, estriol, and ethinylestradiol, was relatively stable in the algal culture, whereas estradiol valerate was hydrolyzed to estradiol and then to estrone within 3 h of incubation. All of the tested estrogens exhibited a degree of partitioning to C. vulgaris; however, the concentrations of estriol, hydroxyestrone, ethinylestradiol, and estradiol valerate were always below the quantification limits. For estradiol and estrone, the partitioning of these estrogens in the algal extracts to the filtrates was <6% of the total amount present. The average concentration factor for estrone was ca. 27; however, the concentration factor for estradiol was not reported since no equilibrium was reached between the aqueous solution and that within the cells due to continuing biotransformation.

Chlorella↗
PubMed2001

Polybrominated diphenyl ether (PBDE) flame retardants.

Polybrominated diphenyl ether, PBDE, flame retardants are now a world-wide pollution problem reaching even remote areas. They have been found to bioaccumulate and there are concerns over the health effects of exposure to PBDEs, they also have potential endocrine disrupting properties. They are lipophilic compounds so are easily removed from the aqueous environment and are predicted to sorb onto sediments and particulate matter or to fatty tissue, aiding their distribution throughout the environment. PBDEs are structurally similar to PCBs and DDT and, therefore, their chemical properties, persistence and distribution in the environment follow similar patterns. Concentrations of PBDEs found in environmental samples are now higher than those of PCBs. Evidence to date demonstrates that PBDEs are a growing problem in the environment and concern over their fate and effects is warranted. The manufacture of reactive and additive flame retardants is briefly discussed and their fate and behaviour in the environment is assessed. PBDE toxicology is reviewed and methods of analysis are evaluated.

Animals↗
PubMed2001

Multivariate analysis of U.K. salt marsh sediment contaminant data with reference to the significance of PCB contamination.

A data set acquired to establish an inventory of pollutants in salt marsh sediments has been evaluated using two numerical techniques, principal component analysis and discriminant analysis. Results indicate that sites proximate to the River Thames exhibit a greater degree of contamination, and numerical analysis supports the hypothesis that the river has been the major source of contaminants to the region. The presence of the contaminants within salt marsh sediments may be of concern due to changes in flood defense techniques. The use of managed realignment, where the line of flood defense is moved back to higher ground which requires only a low, minimal cost, sea-wall protected by newly created salt marsh from former farmland, is not free from problems of historical pollution. Mature salt marsh, laid down during previous decades, may be eroded and reworked within the new coastal geomorphology created by breaching existing seawalls and what were previously considered to be sinks of pollutants may have become sources. However, evaluation of the sediment burden of PCB within the salt marshes of the U.K. Essex coast indicates that they are not likely to be a major source of pollutants should sediments be remobilized during managed realignment programs.

Conservation of Natural Resources↗
PubMed2001

Flood defence in the Blackwater Estuary, Essex, UK: the impact of sedimentological and geochemical changes on salt marsh development in the Tollesbury Managed Realignment site.

Recent changes in the UK's coastal defence strategy have resulted in the introduction of Managed Realignment (MR), a technique which attempts to establish salt marshes on low-lying coastal farmland. This work investigates the impact of MR, in particular on the interactions between sediment movement, changes in heavy metal concentrations and salt marsh development. Pre- and post-inundation samples were collected and analysed between 1995 and 1997. Sediment transport patterns (1996) demonstrated that sediment particles were distributed by tides around the site, resulting in a change in the spatial distribution of the metals which was related to the sediment particle size distribution. Despite the presence of some metal contaminants found within the MR site, vegetated salt marsh has developed since 1997. However, heavy metals such as Cu, Mn, Ni, Pb and Zn exhibited relative depletion in the sediment developing with salt marsh in 1997, which is in agreement with data indicating that concentrations of metals within sediments is related to frequency of tidal inundation. During initial development of the site, sediment transport was the main factor controlling metal distribution, however, subsequently the frequency of tidal inundation became the most significant factor. Further work may allow for prediction of how future MR sites will develop with respect to redistribution of sediments and subsequent transport of contaminants in the dissolved phase.

Conservation of Natural Resources↗
PubMed2001

Conditions influencing the precipitation of magnesium ammonium phosphate.

Struvite precipitation in wastewater treatment works has caused substantial operational problems since the early 1960s. Struvite, magnesium ammonium phosphate hexahydrate (MgNH4PO4 6H2O), is a white inorganic crystalline mineral that precipitates in places with increased turbulence such as pumps, aerators and pipe bends. Batch experiments were conducted to examine the influence of a number of physical and chemical parameters on struvite crystallisation. This was undertaken by dosing a medium of de-ionised water with varying concentrations of Mg2+, NH4+ and PO4(3-) ions. Preliminary experiments found that struvite could be precipitated out of solution at pH 10 and increasing the ion concentration stoichiometrically could increase crystal yield. Increasing the NH4+ concentration increased purity of the precipitate. As reaction time was increased from 1 to 180 min, crystal size was found to increase from 0.1 to 3mm.

Chemical Precipitation↗
PubMedDate not supplied

Removal of struvite to prevent problems associated with its accumulation in wastewater treatment works.

Deposition of struvite within the infrastructure of wastewater treatment works can cause significant operating difficulties. A laboratory-scale, two-stage, continuously stirred tank reactor was developed to remove struvite to prevent problems associated with its deposition. Before any experimental work was conducted, the mixing regime within the system was determined using a pH-tracer response method. Perfect mixing conditions were achieved once the stirring speed reached 500 rpm. Experiments were conducted examining the effects of various process parameters such as retention time, pH, recycling rate, and ammonium concentration. By increasing the hydraulic retention time, the residual magnesium concentration decreased, with the optimum conditions occurring at 125 minutes.

Corrosion↗