Non-target analysis of grab and passive samples from drainage water of a plastic greenhouse district in southern Italy

The number of agricultural catchments covered by plastic greenhouses is growing worldwide. Greenhouses inherently modify the hydrological processes driving the typical contamination flow paths of open field agriculture. Studies investigating the impacts of greenhouses on surface water quality of small catchments with mixed land use are just emerging. In this study, we focused on a plastic greenhouse district in southern Italy of about 10 km², mainly used to produce leafy vegetables. There, we collected grab samples and time-integrated passive samples every two weeks for one year, upstream and downstream of the district. In order to gain a broad knowledge of the impacts of anthropogenic activities on water quality, we performed a non-targeted screening on the samples analyzed by high performance liquid chromatography coupled to high-resolution mass spectrometry.

We found that time-integrated samples are generally richer in detected and identified chemical features than grab samples. On the other hand, grab sampling was more accurate from a quantitative perspective. This highlighted a relevant tradeoff between the two sampling strategies.

Furthermore, we found that the number and the concentration of contaminants, i.e., pesticides and some pharmaceuticals, typically decreased from upstream to downstream. This suggested that contaminants were already present in the incoming water and emphasized the lack of relevant contamination sources from the greenhouse district to the drainage network.

Water quality issues at the upstream site in the summer period, revealed by the non-targeted screening, were putatively attributed to an undiscovered leakage of untreated urban wastewater. The leakage was also supported by an increase in inorganic phosphate concentration from 1 mg/L to 10 mg/L at the upstream location, and eventually confirmed by independent chemical analyses of sea and river water carried out by the regional environmental protection agency.

This study represents the first exploratory campaign to assess the quality of drainage water in the selected greenhouse district, highlighting that the local horticultural greenhouse production does not impact water safety. In this light, drainage can be stored and safely reused in agriculture at the condition that untreated wastewater is promptly detected and diverted. Follow-up studies shall focus on the quality of leachates and groundwater.