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Abstract

The reuse of treated wastewater (TWW) and sewage sludge represents an important practice that supports sustainable agriculture, conserves freshwater resources, and supports environmental sustainability through circular economy principles. However, both matrices can introduce contaminants of emerging concern (CECs) into agroecosystems, potentially affecting soil health, crop production, and food safety, while their environmental fate, plant uptake, and associated risks remain poorly understood.
This thesis investigated the uptake, translocation, and bioaccumulation of selected model CECs, such as pharmaceuticals, personal care product ingredients, industrial chemicals, hormones and pesticides, in tomato plants (Solanum lycopersicum L. cv. Rally) across five experiments representing key wastewater- and sludge-reuse scenarios: (i) a 2020 field experiment with soil-grown tomatoes irrigated with potable water (PW), TWW, or TWW spiked at 0.1 mg L⁻¹ CECs; (ii) a 2022 field experiment with soil-grown tomatoes irrigated with PW, TWW, or PW/TWW spiked at 1 mg L⁻¹; (iii) a 2020 hydroponic experiment using nutrient solution (NS, control) or NS spiked at 0.1 mg L⁻¹; (iv) a 2022 hydroponic experiment using NS, TWW, NS spiked at 0.1 or 1 mg L⁻¹, or TWW spiked at 1 mg L⁻¹; and (v) a peat-substrate experiment using stabilised anaerobically digested (dried) sludge applied at two agronomic rates (to meet N and P requirements), sludge spiked with CECs at the same rates, CEC-spiked peat, or peat amended with non-dried sludge. To support these experiments, different sample preparation methods were optimised and validated for tomatoes, plant tissues, soil, sludge, TWW and PW followed by liquid chromatography coupled to mass spectrometry (LC–MS/MS) analysis. For TWW, a green dispersive micro-solid phase extraction method based on a newly synthesised acrylic copolymer was evaluated and compared with conventional extraction methods.
In the 2020 field experiment, uptake of CECs into edible tissues was minimal: no compounds were detected in fruits under PW or TWW irrigation, and only bisphenol S (BPS) was quantified in fruits irrigated with spiked TWW. In 2020, BPS, bisphenol F (BPF), and naproxen were quantified in tomatoes grown hydroponically in spiked NS. Across various experiments, CEC uptake and translocation were significantly influenced by the compound's physicochemical properties, matrix composition, and cultivation conditions. Under realistic field irrigation conditions (TWW), bioaccumulation in edible tissues was limited, with carbamazepine being the only CEC quantified. In spiked media, acetamiprid, azithromycin, BPS, carbamazepine, clarithromycin, and dimethomorph were above the limit of quantification in tomato fruits, while up to 17 CECs were quantified in roots > leaves > stems.
In the 2022 hydroponic experiment, reduced plant growth was observed, including leaf chlorosis and a poor root system, which led to minimal fruit production (not ripe). However, uptake by roots was extensive, with concentrations reaching up to 118 μg/g for specific compounds. In plant parts, 21 out of 27 CECs were found, with a distribution pattern of roots > leaves > stems > fruits. In fruits, between 6 and 12 CECs were quantified depending on the treatment (TWW or spiked media). In pot experiments with sludge amendment, tomato fruits accumulated a range of CECs, depending on the treatment and whether spiking was applied. In tomato fruits, ibuprofen and triclosan were quantified at the low amendment rate, while caffeine, carbamazepine, ciprofloxacin and ibuprofen were quantified at the high amendment rate. For carbamazepine, the only compound detected in each tissue in spiked treatments, translocation from roots to leaves was highest, followed by stems and fruit.
Across all experiments, dietary exposure assessments indicated that consuming tomatoes grown with TWW irrigation or sludge amendment generally posed limited risks to human health. For the majority of compounds found in fruits, the calculated estimated intake remained below the respective health-based guidance values, for two consumption rates and all evaluated age groups. Carbamazepine, the only CEC detected in soil-grown tomato fruits under realistic TWW irrigation, had an estimated daily intake of nearly half the respective acceptable daily intake (Hazard Quotient up to 0.017), even for vulnerable population groups, such as toddlers. Across all the experiments, risk was identified only for bisphenols (BPS, BPF, and bisphenol A (BPA)), due to the comparison with the tolerable daily intake proposed for BPA, as a conservative approach.
Ecological risk was evident in both soil and peat substrate experiments. Under TWW irrigation, selected CECs, azithromycin and triclocarban, remained in soil up to 30 months after TWW irrigation, and exceeded risk thresholds. In sludge-amended peat, when dried sludge was applied at two levels, risks were identified for five compounds. Drying sludge before amendment resulted in a lower risk compared to adding non-dried sludge, with seven compounds exceeding the risk threshold. The results highlight that the repeated use of TWW and sludge can lead to the accumulation of CECs in soils, facilitating their uptake by plants.
Overall, the thesis contributes to the understanding of the uptake and translocation of CECs in tomato plants. Findings confirm that wastewater irrigation and sludge amendment can lead to CEC uptake in tomato plants; however, accumulation in fruits is generally low and matrix-dependent. This thesis highlights the importance of degradation and sorption processes in TWW, soil, and sludge, which seem to limit the fraction that remains bioavailable for plant uptake. The results support the need for updated regulatory frameworks, improved monitoring of CECs and further research on long-term reuse scenarios to ensure the safe agricultural reuse of wastewater and sludge.