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Cadmium-enriched Sewage Sludge Application to Acid and Calcareous Soils: Relation Between Treatment, Cadmium in Saturation Extracts, and Cadmium Uptake¹

ABSTRACT

The objective of this study was to determine the effect of soil pH on the availability of saturation-extract Cd. Four acid and four calcareous soils were treated with a uniform amount of sewage sludge enriched with different amounts of CdSO₄ to yield soil Cd concentrations ranging from 0.1 to 160 µg Cd/g of sludge-amended soils. These treated soils were placed in plastic containers and cropped for approximately 7 weeks with sweet corn (Zea mays L.), tomato (Lycopersicon esculentum Mill.), and Swiss chard (Beta vulgaris var. ‘cicla’). Shoot weights were obtained as a measure of yields. The concentration of Cd in the shoot (Cd uptake) was taken as a measure of Cd availability.

Saturation extracts from each treated soil (7 Cd rates x 3 replicates x 8 soils) collected at harvest time were analyzed for pH, EC_e, principal soluble anions, and cations with Cu, Cd, Ni, and Zn. The chemical analyses of the saturation extracts were used as input data to calculate the concentration of free ionic Cd (Cd²⁺), the activity of Cd²⁺ (a_Cd²⁺), and the concentration of Cd complexes. These Cd parameters, along with the measured concentration of all Cd forms present in saturation extracts (Cd_T), were compared to Cd concentrations in each of the test plants (µg Cd/g shoot). Results of these comparisons showed: (i) Cd_T was more available in acid than calcareousoils; (ii) Cd uptake by the test plants correlated equally well with the concentration of Cd_T, Cd²⁺, or a_Cd²⁺; and (iii) uptake of Cd was plant-species dependent. Chard and tomato accumulated 2 to 3 times more Cd than corn when grown on the acid soils.

Key Words: soil pollution • soil pH • available Cd • corn • chard • tomato

¹ Contribution from the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92521. Presented before Div. S-4, Soil Sci. Soc. Am., Chicago, Ill., 5 Dec. 1978.

² Soil Scientist and Professors of Soil Science, respectively. Senior author's address is Ultimate Disposal Sect., Wastewater Res. Div., Munic. Environ. Res. Lab., USEPA, Cincinnati, OH 45268.

Received for publication February 5, 1979.