Mol 2 Net Uptake of Different Organic Pollutants by Carrot

In this study the uptake of different organic pollutants, including musk fragrances (tonalide and galaxolide), polybrominated diphenyl ethers (PBDEs), perfluorocarboxylic acids (PFCAs), perfluorosulfonic acids (PFSAs) and perfluorosulfonamide (FOSA) by carrot samples was compared. The bioconcentration factors (BCFs), defined as ratio of the concentration in the dry plant tissue and the concentration in the compost amended soils, were compared and correlation with the water solubility of the target compounds was studied. A good correlation was obtained between the water solubility and the BCFs in the different plant tissues (carrot root peel, root core and leaves). Besides, while the target analytes with the lowest solubility (musk fragrances and PBDEs) tended to accumulate in the peel of the carrot, the most water soluble target analytes (the perfluorinated compounds) tended to translocate to the carrot leaves. . .


Introduction
Under the Urban Wastewater Treatment Directive (UWWTD), towns and cities within the 28 European Union (EU-28) members are required to collect and treat their urban wastewater.The reuse of the sludge is also encouraged, and final disposal to surface waters has been banned (1).However, wastewater treatment plants (WWTPs), also called "biological treatments", are demonstrated not to be effective enough in contaminant removal (2).Not all the chemicals entering the WWPTs are completely degraded and are either removed by sorption and deposition to the final sludge, by volatilization or by discharge onto a surface SciForum http://sciforum.net/conference/mol2net-1water body, if they remain in the wastewater effluent stream (2).
In this sense, contaminants of emerging concern (CECs) have been detected in effluents discharges from municipal and/or industrial wastewater treatment plants (WWTPs), including polybrominated diphenyl ethers (PBDEs), musk fragrances or perfluorinated compounds (2,3).
Land applications of sewage sludge and/or compost derived of them have been adopted worldwide as an option for sludge management.Crops grown in soils amended or irrigated with wastewater containing CECs are exposed to contaminant uptake (4), which then become and entrance of pollutants in the food chain.Within this context, and taking into account that plants form an essential basis of animal and human diet, an evaluation of the uptake and accumulation of potential harmful organic contaminants in plants is of importance for risk assessment.
In this sense, the aim of the present work is to study the uptake in terms of BCFs of different organic pollutants, including musk fragrances (tonalide and galaxolide), PBDEs, perfluorocarboxylic acids (PFCAs), perfluorosulfonic acids (PFSAs) and perfluorooctanosulfonamide (FOSA) by different carrot compartments (peel, core and leaves) and to evaluate the correlation between BCFs and the target analytes water solubility. .
It should also be highlighted, while the target analytes with the lowest solubility (musk fragrances, AHTN and HHCB, and PBDEs, BDE-138 and BDE-209) tended, in general, to accumulate in the peel of the carrot, the most water soluble target analytes (PFOS and PFOA as examples) tended to translocate to the carrot leaves (see BCFs included in Table 1).However, as can be clearly observed from Table 1, while BDE-138 accumulated exclusively in the peel, BDE-209 accumulated mainly in the leaves (BCFleaves) when present at a low concentration.
Accumulation in the leaves could be due to translocation after root uptake or by foliar uptake http://sciforum.net/conference/mol2net-1from the air.According to the values obtained from the blanks, no appreciable contribution from foliar uptake was observed for any of the target analytes and, thus, foliar uptake was discarded.

Plant Cultivation
Pots (n=2) with 2 kg of the (95:5) soil:compost mixtures were sown with previously germinated (~14 days) carrot seeds.For germination, petri dishes were covered with moistened filter paper and the seeds were evenly distributed in the petri dish.Afterwards, seeds were covered with another piece of moistened filter paper.The number of plants per pot was 3−4.
Control (n=1) plants of carrots grown in the non-fortified compost amended soil 2.4 mixture were placed in between the fortified amended soil pots.The cultivation of the carrot was performed under controlled greenhouse conditions.
Temperature was set to 25 °C during the day and at 18 °C during the night with a 14-h day length and a relative humidity of 50 % and 60 % during the day and overnight, respectively, and they were regularly watered with distilled water and Hoagland nutritive solution (5).Carrots were harvested during a period of three months reflecting the minimum time to produce relatively mature crops and all plants per pot were collected and pooled to one sample.Each plant was dissected into roots (peel and core) and leaves.Fresh weight of all plant fractions was recorded, followed by rinsing with tap water.Carrots were peeled with a vegetable peeler (depth of ~2 mm).

Sample treatment and analysis
Carrot samples (peel, core and leaves) were freeze-dried using a Cryodos-50 laboratory freeze-dryer (Telstar Instrumat, Sant Cugat del Valles, Barcelona, Spain).In the case of the compost amended soil, this was air-dried for approx.48 hours.Both, the dried plant and compost amended soil samples were stored at -20

Conclusions
It has been demonstrated that uptake of several organic pollutants is dependent on their water solubility and that the BCFs in the different carrot compartments is exponentially related to the logarithm of the water solubility of the target analytes.A dramatically bioconcentration increase for the analytes (PFHxPA, PFPeA and PFBA) with a water solubility higher than 8 was observed.In general, while the target analytes with the lowest solubility tended to accumulate in the carrot peel, the most water soluble target analytes tended to translocate to the leaves.