Uptake and translocation of perfluoroalkyl acids (PFAAs) in hydroponically grown red chicory (Cichorium intybus L.): Growth and developmental toxicity, comparison with growth in soil and bioavailability implications

Short-chain perfluoroalkyl acids (PFAAs) have shown a high potential for plant (crop) uptake, making them possibly significant contributors to the total dietary exposure to PFAAs. The plant uptake of PFAAs is a complex process that needs better characterization, as it does not only depend on perfluoroalkyl chain length, but also on their polar terminal group, on the plant species and the exposure media. Here, a plant uptake study with nine perfluoroalkyl acids (PFAAs) was carried out under the hydroponic (soilless) exposure conditions. Red chicory was grown in a nutrient solution, spiked with PFAAs mixture at three different concentrations (i.e. 62.5, 125 and 250 μg/L), in order to extend the range of levels tested and reported in the literature so far. Bioaccumulation metrics and transpiration stream concentration factors (TSCFs) were employed for the plant uptake characterization and consequent comparison with the results of soil uptake experiment we previously performed with the same crop. The results showed that calculated root concentration factors (RCFs) increase with PFAA chain length, while the opposite chain length dependence was present for shoots. Plants from two treatments with the highest PFAAs concentrations manifested physiological changes (discoloration, inhibited roots and leaves growth), despite of the used exposure concentrations being much lower than previously published phytotoxicity thresholds. A comparison among RCFs and TSCFs derived from hydroponic and from the soil experiment has emphasized their different magnitudes and PFAAs chain length dependence patterns. They could not be ascribed only to soil sorption as a process decreasing PFAAs bioavailability for plants, but also to developmental differences between the root systems formed in soil and in nutrient solution and to the potential competitive PFAAs sorption to roots in hydroponics. The interchangeable use of bioaccumulation and translocation parameters derived in hydroponic and soil systems would lead to erroneous conclusions and plant uptake predictions.

Model-based analysis of the uptake of perfluoroalkyl acids (PFAAs) from soil into plants

Perfluoroalkyl acids (PFAAs) bioaccumulate in crops, with uptake being particularly high for short-chain PFAAs that are constantly transported with transpiration water to aerial plant parts. Due to their amphiphilic surfactant nature and ionized state at environmental pH, predicting the partitioning behavior of PFAAs is difficult and subject to considerable uncertainty, making experimental data highly desirable. Here, we applied a plant uptake model that combines advective flux with measured partition coefficients to reproduce the set of empirically derived plant uptake and soil-partitioning data for nine PFAAs in red chicory, in order to improve the mechanistic understanding and provide new insights into the complex uptake processes. We introduced a new parameter for retarded uptake (R) to explain the slow transfer of PFAA across biomembranes of the root epidermis, which has led to low transpiration stream concentration factors (TSCFs) presented in literature so far. We estimated R values for PFAAs using experimental data derived for red chicory and used the modified plant uptake model to simulate uptake of PFAA into other crops. Results show that this semi-empirical model predicted PFAAs transport to shoots and fruits with good accuracy based on experimental root to soil concentration factors (RCF_dw) and soil to water partition coefficients (K_d) as well as estimated R values and plant-specific data for growth and transpiration. It can be concluded that the combination of rather low K_d with high RCF_dw and the absence of any relevant loss are the reason for the observed excellent plant uptake of PFAAs.

Uptake and translocation of perfluoroalkyl acids (PFAA) in red chicory (Cichorium intybus L.) under various treatments with pre-contaminated soil and irrigation water

Perfluoroalkyl acids (PFAAs), particularly short-chained ones, have high potential for crop uptake, posing a threat to human health in contaminated areas. There is a scarcity of studies using contaminated water as the medium for PFAAs delivery to crops, and a lack of data on the partitioning of PFAA mixtures in growing media. In this context, a controlled experimental study was carried out in a greenhouse to investigate the uptake of a PFAA mixture into red chicory, a typical crop from a major PFAA contamination hot-spot in northern Italy, under treatments with environmentally relevant concentrations in spiked irrigation water and soil, separately and simultaneously. To our knowledge, this is the first study involving multiple exposure media and laboratory adsorption/desorption batch tests as a way of assessing the decrease in the bioavailability of PFAAs from soil. Exposure concentrations for each of the 9 utilized PFAAs were 0, 1, 10 and 80 µg/L in irrigation water and 0, 100 and 200 ng/gdw in soil, combined into 12 treatments. The highest bioaccumulation was measured for PFBA in roots (maximum of 43 µg/gdw), followed by leaves and heads of the chicory plants in all treatments, with the concentrations exponentially decreasing with an increasing PFAA chain length in all plant compartments. The use of irrigation water as the delivery medium increased the transport of PFAAs to the aerial chicory parts, long-chain substances in particular. Additionally, the distribution of PFAAs in the soil was assessed by depth and compared with laboratory measured soil-water equilibrium partition coefficients, revealing only partial dependency of PFAAs bioavailability on the adsorption in soil.

Deriving predicted no-effect concentrations (PNECs) for emerging contaminants in the river Po, Italy, using three approaches: Assessment factor, species sensitivity distribution and AQUATOX ecosystem modelling

Over the past decades, per- and polyfluoroalkyl substances (PFASs) found in environmental matrices worldwide have raised concerns due to their toxicity, ubiquity and persistence. A widespread pollution of groundwater and surface waters caused by PFASs in Northern Italy has been recently discovered, becoming a major environmental issue, also because the exact risk for humans and nature posed by this contamination is unclear. Here, the Po River in Northern Italy was selected as a study area to assess the ecological risk posed by perfluoroalkyl acids (PFAAs), a class of PFASs, considering the noticeable concentration of various PFAAs detected in the Po waters over the past years. Moreover, the Po has a large environmental and socio-economic importance: it is the largest Italian river and drains a densely inhabited, intensely cultivated and heavily industrialized watershed. Predicted no-effect concentrations (PNECs) were derived using two regulated methodologies, assessment factors (AFs) and species sensitivity distribution (SSD), which rely on published ecotoxicological laboratory tests. Results were compared to those of a novel methodology using the mechanistic ecosystem model AQUATOX to compute PNECs in an ecologically-sound manner, i.e. considering physical, chemical, biological and ecological processes in the river. The model was used to quantify how the biomasses of the modelled taxa in the river food web deviated from natural conditions due to varying inputs of the chemicals. PNEC for each chemical was defined as the lowest chemical concentration causing a non-negligible yearly biomass loss for a simulated taxon with respect to a control simulation. The investigated PFAAs were Perfluorooctanoic acid (PFOA) and Perfluorooctanesulfonic acid (PFOS) as long-chained compounds, and Perfluorobutanoic acid (PFBA) and Perfluorobutanesulfonic acid (PFBS) as short-chained homologues. Two emerging contaminants, Linear Alkylbenzene Sulfonate (LAS) and triclosan, were also studied to assess the performance of the three methodologies for chemicals whose ecotoxicology and environmental fate are well-studied. The most precautionary approach was the use of AFs generally followed by SSD and then AQUATOX, except for PFOS, for which AQUATOX yielded a much lower PNEC compared to the other approaches since, unlike the other two methodologies, it explicitly simulates sublethal toxicity and indirect ecological effects. Our findings highlight that neglecting the role of ecological processes when extrapolating from laboratory tests to ecosystems can result in under-protective threshold concentrations for chemicals. Ecosystem models can complement existing laboratory-based methodologies, and the use of multiple methods for deriving PNECs can help to clarify uncertainty in ecological risk estimates.