Measuring and Modelling the Plant Uptake and Accumulation of Synthetic Organic Chemicals: With a Focus on Pesticides and Root Uptake

Abstract

Plant uptake of synthetic organic chemicals involves the transport of a xenobiotic into the plant cells via the roots or shoots. There is little evidence to demonstrate plants enhance the release of pesticides from recalcitrant fractions in the soil. In the limited studies available, plant uptake is effectively predicted by the bioavailable fraction recovered from passive samplers and mild extractants. These two areas will be fruitful areas for future research. Once the compound enters the plant, there are several potential transport routes prior to translocation to the shoots or accumulation within the roots. Modelling the plant uptake of organic chemicals allows for the assessment of risks to human health. There is currently a significant amount of debate within the research community as to the preferred way for quantifying uptake and most appropriate experimental method for measuring uptake. The use of transpiration stream concentration factor (TSCF) predicted by the octanol-water partition coefficient (log KOW) has long been the dominant model; however, recent research has suggested a move away from these predictive relationships. Many studies have been conducted with approximately 200 data points being reported in the peer-reviewed literature; however, statistical analysis has shown that we are no closer to establishing a definitive algorithm to predict plant uptake of organic chemicals. Whilst log KOW could still be an important predictor, other physical-chemical properties, such as molecular weight and hydrogen bond donors, could also play a role. Currently, there is ongoing debate as to whether TSCF is the most suitable measure of plant uptake as it only considers the fraction of the compound that has been translocated to the above-ground plant parts. The plant uptake factor (PUF) considers uptake into the whole plant by measuring the change in concentration of the compound in the uptake solution against the change in volume and may provide a more accurate uptake value as a result. Despite this, both the use of further physical-chemical properties and PUF are relatively new and require rigorous testing by researchers to establish their suitability.