Biological effects of unburnt coal in the marine environment

Unburnt coal is a widespread and sometimes very abundant contaminant in marine environments. It derives from natural weathering of coal strata and from anthropogenic sources including the processing of mined coal, disposal of mining wastes, erosion of stockpiles by wind and water, and spillage at loading and unloading facilities in ports. Coal is a heterogeneous material and varies widely in texture and content of water, carbon, organic compounds and mineral impu- rities. Among its constituents are such potential toxicants as polycyclic aromatic hydrocarbons (PAHs) and trace metals/metalloids. When present in marine environments in sufficient quantities, coal will have physical effects on organisms similar to those of other suspended or deposited sediments. These include abrasion, smothering, alteration of sediment texture and stability, reduced availability of light, and clogging of respiratory and feeding organs. Such effects are relatively well documented. Toxic effects of contaminants in coal are much less evident, highly dependent on coal composition, and in many situations their bioavailability appears to be low. Nevertheless, the presence of contaminants at high concentrations in some coal leachates and the demonstration of biological uptake of coal-derived contaminants in a small number of studies suggest that this may not always be the case, a situation that might be expected from coal's heterogeneous chemical composition. There are surprisingly few studies in the marine environment focusing on toxic effects of contaminants of coal at the organism, population or assemblage levels, but the limited evidence indicating bioavailability under certain circumstances suggests that more detailed studies would be justified.