Plastics debris in the marine environment, including resin pellets, fragments and microscopic plastic fragments, contain organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons, petroleum hydrocarbons, organochlorine pesticides (2,2 0 -bis(p-chlorophenyl)-1,1,1-trichloroethane, hexachlorinated hexanes), polybrominated diphenylethers, alkylphenols and bisphenol A, at concentrations from sub ng g -1 to mg g -1. Some of these compounds are added during plastics manufacture, while others adsorb from the surrounding seawater. Concentrations of hydrophobic contaminants adsorbed on plastics showed distinct spatial variations reflecting global pollution patterns. Model calculations and experimental observations consistently show that polyethylene accumulates more organic contaminants than other plastics such as polypropylene and polyvinyl chloride. Both a mathematical model using equilibrium partitioning and experimental data have demonstrated the transfer of * Author for correspondence (shige@cc.tuat.ac.jp).Electronic supplementary material is available at http://dx.doi.org/rstb20080284 or via http://rstb.royalsocietypublishing.org.One contribution of 15 to a Theme Issue 'Plastics, the environment and human health'.

Research on the environmental impacts of black carbon has focused largely on sorption. Besides being a strong geosorbent, black carbon is redox-active and may facilitate abiotic and microbial transformation. Using a wood-derived black carbon (biochar) and the bacterium Geobacter metallireducens (GS-15), we showed that air-oxidized biochar served as an electron acceptor to enable acetate oxidation, and that chemically or biotically reduced biochar served as an electron donor for nitrate reduction. The bioavailable (to GS-15) electron storage capacities (ESCs) of the biochar, estimated on the basis of acetate oxidation and nitrate reduction, were 0.85 and 0.87 mmol e–/g, respectively, comparable to the ESCs of humic substances and other biochars measured electrochemically. We propose that black carbon should be regarded as a rechargeable reservoir of bioavailable electrons in anaerobic environments. The redox cycling of biochar in natural and engineered systems and its impact on microbial processes and contaminant fate merit further investigations.

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Factors controlling organic contaminant sorption to common plastics in municipal solid waste were identified. Consumer plastics [drinking water container, prescription drug bottle, soda bottle, disposable cold cup, computer casing, furniture foam, carpet, vinyl flooring, formica sheet] and model polymers [high-density polyethylene (HDPE), medium-density polyethylene, low-density polyethylene, poly(vinyl chloride) (PVC)] were characterized by X-ray diffractometry, differential scanning calorimetry, and elemental analysis. The material characterization was used to interpret batch isotherm and kinetic data. K(p) values describing toluene sorption to rubbery or "soft" polymers could be normalized by the amorphous polymer fraction (f(amorphous)) but not by the organic carbon fraction (f(oc)). Diffusion coefficients (D) describing the uptake rate of toluene by rubbery plastics (HDPE, drinking water container, prescription drug bottle) were similar (D approximately 10(-10) cm(2)/s), indicating that pure HDPE can be used as a model for rubbery plastics. Toluene diffusivity was similar among glassy or "hard" plastics (PVC, soda bottle, computer casing, disposable cold cup; D approximately 10(-12) cm(2)/s) but lower than for rubbery plastics. Plastics in landfills are potential sinks of hydrophobic organic contaminants (HOCs) because of their higher affinity for HOCs compared to lignocellulosic materials and the slow desorption of HOCs from glassy plastics.