Carbon, nitrogen and heavy metal dynamics in long-term wastewater irrigated Mexican soils.

In column experiments of Mexican wastewater irrigated soils the effects of changing water quality (untreated = UT, primary = PT and tertiary treated = TT wastewater) on carbon, nitrogen and heavy metal dynamics were investigated. In the column effluents the nitrate concentrations varied between 141-683 mg l-1. The total amount of leached TOC decreased in the order UT > PT > TT. Outflow concentrations of Pb ranged from 31.6-166.5 micrograms l-1 and of Cu from 31.2-146.8 micrograms l-1. Irrigation water quality influenced the Pb but not the Cu efflux. Cu seemed to be co-transported with TOC by preferential flow whereas there was no correlation of Pb and TOC concentrations in the effluents. The possibility of Pb transport through preferential flow paths is discussed.