Case Study 3: Study of the uptake contaminants in vegetable crops irrigated with reclaimed water

In recent decades, water scarcity has escalated due to climate change and increasing water consumption by the human population. To mitigate this, reusing treated water from secondary wastewater treatment plants (WWTPs) for crop irrigation has gained popularity. PROMISCES has undertaken a study to assess the effects of this practice. This study has quantified PMT uptake by lettuce irrigated with reclaimed water, comparing it with crop uptake factors for PFAS and other iPM(T)s. Lettuce leaves were analysed following irrigation with reclaimed water treated through an electrochemical advanced oxidation process (EAOP) combined with a constructed wetland (RW), alongside secondary effluent (WW) and bottled water (BW) as positive and negative controls, respectively. Crop productivity, quality, and metabolomics were monitored to assess the effects of PMT uptake through the plant system. Additionally, a human health risk assessment was conducted to evaluate the potential risk to consumers.

The study first examined the presence of contaminants in soil and irrigation water. As expected, various ubiquitous phthalates - though not the main target compounds - including diethyl phthalate were detected in all irrigation waters, including bottled water. Additionally, both diethyl and dibutyl phthalates were found at notable concentrations in soil, wastewater, and reclaimed water, underscoring the widespread presence of phthalate compounds in the environment. Interestingly, pharmaceuticals and pesticides appeared to be more closely associated with wastewater sources. No PFAS were detected in bottled water or soil.

After 41 days of cultivation, out of the entire set of PFAS analysed, only two acids and three sulfonates were detected in the samples. The sulfonates PFHxS, PFOS and 6:2 FTS were the most frequently identified, consistent with the higher log Kow values, indicating greater potential for uptake and accumulation. Out of the 41 iPM(T)s evaluated, 16 compounds were detected in the lettuce samples. The antidepressant venlafaxine and its metabolite O-desmethylvenlafaxine, as well as the drug of abuse MDMA and the pesticide carbendazim, were only found in lettuce samples irrigated with wastewater, suggesting the combined technology successfully minimized their presence in reclaimed water and the irrigated crops. A different trend emerges for certain industrial chemicals, such as 2-ethylhexyl diphenyl phosphate and bis(2-ethylhexyl) amine, shows similar concentrations across all irrigation types, including in the control samples. These results are consistent with the detection of phthalates in all irrigation waters and some PMTs from industrial application found in the soil.

Regarding crop yield and metabolomics, no significant differences were observed despite varying irrigation treatments. However, wastewater irrigated crops exhibited increased lipid and chlorophyll contents, a finding that could indicate a stress response. In terms of human health implications, PFAS uptake data revealed that samples irrigated with direct wastewater exceeded the tolerable weekly intake for PFAS (4.4 ng/kg/week). In contrast, the use of reclaimed water reduced consumer risk, highlighting the necessity of developing advanced water treatment technologies to combine a more closed water cycle and safer agricultural practices.