Organic carbon normalisation of PCB, PAH and pesticide concentrations in suspended solids

The equilibrium partitioning concept for hydrophobic organic compounds (HOCs) predicts that organic carbon (OC) normalised or organic matter (OM) normalised HOC concentrations are approximately the same for different solid types sampled at the same time from the same surface water. This hypothesis was tested for polyaromatic hydrocarbon (PAH), polychlorobiphenyl (PCB) and pesticide concentrations in settling solids (sediment trap) and suspended solids (continuous flow centrifuge) taken from Lake Volkerak and Lake Zoom (The Netherlands). It was found that settling solids had significantly higher OC normalised, or OM normalised HOC concentrations than suspended solids. Also, the degree of mineralisation as quantified by the OC---N atomic ratio of the organic material was significantly higher for the settling solids. The higher degree of mineralisation explains the higher normalised HOC concentrations in the settling solids. It was concluded that the ageing of organic matter during settling in the water column or after burial in sediments, may cause the increased fixation of HOCs onto organic particles.