Evaluation of Chemical Impacts of Rice Irrigated with Urban Treated Wastewater

Improving practices of water saving in irrigation is a priority facing global climate changes. To cope with water scarcity, the irrigation with treated wastewater (TWW) is becoming a solution, posing however several health and environmental risks on agricultural fields. This preliminary study aimed to assess the physicochemical impacts of rice irrigated with TWW applied with a subsurface drip irrigation (SDI) system, focusing the rice food, soil and environmental safety. Normal water and flooding was used as a reference for comparison. The experimental scheme considered three treatments with five repetitions, namely the TWW irrigation with SDI, the normal water with SDI, and the flooded irrigation with normal water. The pots filled with 15 L of soil, sowed with a local traditional rice variety, were kept outdoors. The fertilization scheme followed the usual one under field conditions. The irrigation frequency varied from three to five times a week. Measurements of physicochemical properties of irrigation water, drainage and rice grain were carried out, according to the analytical reference methods. Results showed that the irrigation with TWW rises the electric conductivity of drainage water, but that the rice grain does not present increased risks to public health due to the low content of arsenic, cadmium, lead and mercury. However, the irrigation method must be adapted to a SDI to avoid human and animal contact with putative contaminants present in this water and thus safeguarding Environmental and Food Safety. Long term soil effects of TWW, including winter percolation, will be assessed in the future.