Statewide Evaluation of Trace Element Accumulation from Long-Term Disposal of Wastewater
This report provides the first comprehensive field evaluation of trace element accumulation from land disposal of wastewater in the state of California. Past effects of long-term reuse practices were studied to assist in policy decisions regarding wastewater reuse and future uses of lands which have received wastewater.
In the present study twenty reuse sampling sites were selected on the basis of the following criteria: length of time the site has received wastewater, amount and manner of application, quality of wastewater applied, and the availability of historical data on trace element content in wastewater effluent. Each site was visited once during the two year study. Both soil and vegetation samples were collected from each site. These samples were analyzed for Cd, Cu, Pb, Ni and Zn content. Soil samples were also analyzed for pH, CEC and water content.
This study project indicated that 9% of the fields investigated showed an accumulation of trace elements from reuse practices. Metal enrichment was confined to upper layers of soil, but penetrated into the soil column depending on soil type and rate of wastewater application. Translocation of metals into plants from these sites was dependent on the plant species as well as the given metal. Cadmium and Zn were the most mobil [sic] of the metals tested.
This investigation concludes that land application of wastewater provides useful irrigation waters under most circumstances. Metal Accumulation was noted only for fields which had not been ploughed. Filling the soil most likely diluted the amount of metal in a given cm core by spreading it over the depth of tillage. Increased chances for significant elevation of soil metal occurs when the level of treatment is reduced below the secondary. When the application rate is increased or if a high percentage of the wastewater is from industrial sources.