Effect of produced water treatment technologies on irrigation-induced metal and salt accumulation in wheat (Triticum aestivum) and sunflower (Helianthus annuus).

Produced water (PW), a wastewater resulting from hydraulic fracturing and oil and gas production, has been utilized in arid regions for irrigation purposes and potentially presents a new water source for crop irrigation in areas of increasing water scarcity. However, there is a potential for both synthetic and geogenic contaminants in these waters to accumulate in irrigated food crops. This study assessed how water treatment technologies targeted at removal of salinity (i.e., total dissolved solids) and organic chemical content (i.e., dissolved organic carbon) from PW to achieve agricultural irrigation standards altered the impact of inorganic contaminants and nutrient uptake on two salt-tolerant food crops, sunflower (Helianthus annuus) and wheat (Triticum aestivum). The impacts of the treatment technologies on inorganic contaminant loadings in the irrigated soils were also assessed. Treatment technologies to improve PW quality decreased the adverse impacts on plant health; however, plant health was more affected by dilutions of PW than by the treatment technologies employed. Phenotypically, plants irrigated with 90% dilution (low) treatment groups, regardless of treatment technology, were comparable to controls; however, plants watered with high proportions (50%) of raw or treated PW displayed stunted growth, with reduced height and leaf area, and sunflower seed saw 100% yield loss. Although phenotypically similar, plants of the low treatment groups exhibited changes in the ionome, illustrating the influence of PW on plant uptake, translocation, and accumulation of metals, salts, and micronutrients. In addition, bioavailability of metals and nutrients was impacted by the unique and complex PW matrix: bioconcentration factors traditionally used to evaluate risk may therefore over or underestimate accumulation.