9. Uptake of Organic Contaminants from Soil into Vegetables and Fruits

Contaminants may enter vegetables and fruits by several pathways: by uptake with soil pore water, by diffusion from soil or air, by deposition of soil or airborne particles, or by direct application. The contaminant-specific and plant-specific properties that determine the importance of these pathways are described in this chapter. A variety of models have been developed, specific for crop types and with steady-state or dynamic solutions. Model simulations can identify sensitive properties and relevant processes. Persistent, polar (log K _OW < 3) and non-volatile (K _AW < 10^–6) contaminants have the highest potential for accumulation from soil, and concentrations in leaves may be several hundred times higher than in soil. However, for most contaminants the accumulation in vegetables or fruits is much lower. Lipophilic (log K _OW > 3) contaminants are mainly transported to leaves by attached soil particles, or from air. Volatile contaminants have a low potential for accumulation because they quickly escape to air. Experimental data are listed that support these model predictions, but underline also the high variability of accumulation under field conditions. Plant uptake predictions are uncertain, due to the immense variation in environmental and plant physiological conditions. Uptake of organic contaminants into vegetables and fruits may lead to human health risks, but it may also be used to delineate subsurface plumes and monitor Natural Attenuation. Most models mentioned in this chapter are freely available from the authors.