Mark A. Browne

Accumulation of Microplastic on Shorelines Woldwide: Sources and Sinks

Plastic debris <1 mm (defined here as microplastic) is accumulating in marine habitats. Ingestion of microplastic provides a potential pathway for the transfer of pollutants, monomers, and plastic-additives to organisms with uncertain consequences for their health. Here, we show that microplastic contaminates the shorelines at 18 sites worldwide representing six continents from the poles to the equator, with more material in densely populated areas, but no clear relationship between the abundance of miocroplastics and the mean size-distribution of natural particulates. An important source of microplastic appears to be through sewage contaminated by fibers from washing clothes. Forensic evaluation of microplastic from sediments showed that the proportions of polyester and acrylic fibers used in clothing resembled those found in habitats that receive sewage-discharges and sewage-effluent itself. Experiments sampling wastewater from domestic washing machines demonstrated that a single garment can produce >1900 fibers per wash. This suggests that a large proportion of microplastic fibers found in the marine environment may be derived from sewage as a consequence of washing of clothes. As the human population grows and people use more synthetic textiles, contamination of habitats and animals by microplastic is likely to increase.

Spatial Patterns of Plastic Debris along Estuarine Shorelines

The human population generates vast quantities of waste material. Macro (>1 mm) and microscopic (<1 mm) fragments of plastic debris represent a substantial contamination problem. Here, we test hypotheses about the influence of wind and depositional regime on spatial patterns of micro- and macro-plastic debris within the Tamar Estuary, UK. Debris was identified to the type of polymer using Fourier-transform infrared spectroscopy (FT-IR) and categorized according to density. In terms of abundance, microplastic accounted for 65% of debris recorded and mainly comprised polyvinylchloride, polyester, and polyamide. Generally, there were greater quantities of plastic at downwind sites. For macroplastic, there were clear patterns of distribution for less dense items, while for microplastic debris, clear patterns were for denser material. Small particles of sediment and plastic are both likely to settle slowly from the water-column and are likely to be transported by the flow of water and be deposited in areas where the movements of water are slower. There was, however, no relationship between the abundance of microplastic and the proportion of clay in sediments from the strandline. These results illustrate how FT-IR spectroscopy can be used to identify the different types of plastic and in this case was used to indicate spatial patterns, demonstrating habitats that are downwind acting as potential sinks for the accumulation of debris.

A multibiomarker approach to environmental assessment.

Incorporation of ecologically relevant biomarkers into routine environmental management programs has been advocated as a pragmatic means of linking environmental degradation with its causes. Here, suites of biomarkers, devised to measure molecular damage, developmental abnormality and physiological impairment, were combined with chemical analysis to determine exposure to and the effects of pollution at sites within Southampton Water (UK). Test species included a filter feeder, a grazer, and an omnivore to determine the sensitivity of organisms occupying different trophic levels. Linear regression confirmed a significant association between incidence of intersex in Littorina littorea and tributyltin (TBT) concentrations (R2 = 0.954) and between PAH metabolites in Carcinus maenas urine and PAHs in sediments (R2 = 0.754). Principal component analysis revealed a gradient of detrimental impact to biota from the head to the mouth of the estuary, coincident with high sediment concentrations of heavy metals, PAHs, and biocides. Multidimensional scaling identified C. maenas as the organism most sensitive to contamination. Carboxylesterase activity, metallothionein and total haemolymph protein were the most discriminating biomarkers among sites. This holistic approach to environmental assessment is encouraged as it helps to identify the integrated impact of chemical contamination on organisms and to provide a realistic measure of environmental quality.

Rapid assessment of organophosphorous/carbamate exposure in the bivalve mollusc Mytilus edulis using combined esterase activities as biomarkers.

Carboxylesterases in bivalve molluscs exhibit greater sensitivity to organophosphorous and carbamate pesticides than acetylcholinesterase and are present at higher levels. The aim of the present study was to combine measurement of both acetylcholinesterase and carboxylesterase activities in the marine bivalve Mytilus edulis in order to detect the effects of pesticide exposure. Spectrophotometric assays in microtitreplate format were optimised for use with M. edulis haemolymph and tissue homogenate samples. This permitted the nature and distribution of the enzymes to be determined. One predominant pharmacological form of activity consistent in its patterns of activation and inhibition with acetylcholinesterase was identified in the haemolymph with an apparent K(m) for acetylthiocholineiodide of 1.33 mM. Carboxylesterase activity in the tissues was characterised by its preferential hydrolysis of the substrate analogue phenylthioacetate. Concentration-dependent inhibition of both activities was demonstrated following in vitro incubation with diisopropylfluorophosphate (DFP), paraoxon and eserine in the range 0.1-3.0 mM. When M. edulis (n=10) were exposed for 24 h to concentrations of eserine or paraoxon of 0.05-1.0 mM, the percentage inhibition of acetylcholinesterase was in each case greater than for carboxylesterase and reached statistical significance at lower concentrations. In all exposures, a proportion of carboxylesterase activity was present which remained resistant to inhibition by either organophosphorous or carbamate compounds. The ecotoxicological significance of these findings for the environmental monitoring of pesticide exposure is discussed.

Spatial and Temporal Patterns of Stranded Intertidal Marine Debris: Is There a Picture of Global Change?

Floating and stranded marine debris is widespread. Increasing sea levels and altered rainfall, solar radiation, wind speed, waves, and oceanic currents associated with climatic change are likely to transfer more debris from coastal cities into marine and coastal habitats. Marine debris causes economic and ecological impacts, but understanding the scope of these requires quantitative information on spatial patterns and trends in the amounts and types of debris at a global scale. There are very few large-scale programs to measure debris, but many peer-reviewed and published scientific studies of marine debris describe local patterns. Unfortunately, methods of defining debris, sampling, and interpreting patterns in space or time vary considerably among studies, yet if data could be synthesized across studies, a global picture of the problem may be avaliable. We analyzed 104 published scientific papers on marine debris in order to determine how to evaluate this. Although many studies were well designed to answer specific questions, definitions of what constitutes marine debris, the methods used to measure, and the scale of the scope of the studies means that no general picture can emerge from this wealth of data. These problems are detailed to guide future studies and guidelines provided to enable the collection of more comparable data to better manage this growing problem.

AGGREGATION AS A DEFENSE: LIMPET TENACITY CHANGES IN RESPONSE TO SIMULATED PREDATOR ATTACK

Defenses against predators may be physiological, morphological, behavioral, or combinations thereof and are nearly always induced, at least in part, by prey perception of predation risk. One antipredation behavior is to group; however the way in which this translates into a reduction in risk to an individual is not fully understood. Here we demonstrate a novel aspect of grouping as a defense, using aggregated limpets (Patella vulgata) as a test system. Although not having experienced the predator directly, potential prey in aggregations detect the vibrations of an attack on a group member and reduce their vulnerability to predation. This effect travels further and lasts longer than would be expected. Our results imply that, for a prey showing a mix of distributions (some solitary and some aggregated), aggregations may probably be easier to find but actually represent a single predation opportunity.

Effect of extraction-method, period of incubation and tidal emersion on the viability of haemocytes from oysters.

The impacts of pollution on marine organisms are often investigated using the viability of their haemocytes. Although this assay is routinely used in monitoring, field and laboratory experimentation, there has been less effort in further optimizing procedures to reduce artefacts and facilitate sampling over large geographic areas. Using the oyster Saccostrea glomerata as a model species, we investigated the effects of different techniques for extracting haemolymph, period of incubation with dye and emersion-time (e.g. tidal-state) on the viability of haemocytes. Collecting haemocytes with a syringe, through a drilled hole in the shell, increased the viability of haemocytes by almost 50%. While emersion-time and incubating haemocytes with the dye for up to 4 h did not affect viability. This simple in situ approach provides a less destructive method for extracting haemocytes, allowing their viability to be measured as part of large-scale experiments without jeopardizing the surrounding assemblage of animals and plants.