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Accumulation of Heavy Metals in Arid-Zone Soils Irrigated with Treated Sewage Effluents and Their Uptake by Rhodes Grass¹

ABSTRACT

Prolonged commercial irrigation with treated sewage effluents from rural sources resulted in accumulation of heavy metals in the top 10- to 15-cm layer of the soil in three commercial fields. Statistically significant differences were found for total content and extractable fraction of Cd in all three soils, and for Cu, Ni, and Pb in clay soils by comparing these fields and adjacent ones irrigated with normal water. Chromium concentration differences were not statistically significant. As a result, there was some increase in the concentration of these elements in Rhodes grass (Chloris gayana Kunth.) grown in the sewage-effluent-irrigated fields as compared with the grass grown in the fields irrigated with normal water. The increase, although statistically significant, was slight, even in the field that had been irrigated with sewage effluents for up to 28 years. The uptake of the various metals, as assessed by the enrichment factor (EF = µg element g^–1 plant/µg element g^–1 soil), tended to diminish with an increase in the specific surface area of the soil. This was particularly pronounced with the more labile of the elements studied—Cd, Cu, and Ni—and less so for Pb and Cr. The uptake of a given element appears to be largely determined by its solubility in the soil solution and can be generally predicted by its ionic potential. The relative magnitude of the enrichment factor established for Rhodes grass is in the following order: Cu > Cd > Pb > Ni >> Cr.

Key Words: sewage • treated effluent • enrichment factor

¹ Contribution of the Seagram Centre for Soil and Water Sciences, The Hebrew University, P.O. Box 12, Rehovot, and The Soil and Plant Laboratories, Ministry of Agriculture, Hefer Valley, Israel.

² Professor of Soil Science and Senior Soil Chemist, respectively, Seagram Centre for Soil and Water Sciences.

³ Head and Chemist, respectively, Soil and Plant Laboratories, Ministry of Agriculture, Hefer Valley, Israel.

Received for publication October 23, 1979.