Cadmium Solubility and Sorption in a Long‐Term Sludge‐Amended Arable Soil

Abstract

Cadmium solubility and sorption in an arable clay loam soil that had received sewage sludge for 41 years were compared to an unsludged control in batch studies. Soil pH dominated Cd sorption, explaining >92% of the variation in Kd values in both treatments. At any pH, Cd sorption was apparently slightly but significantly (p < 0.05) smaller in the sludge-amended soil compared to the control, even though the organic carbon content was 70% larger and the ammonium oxalate-extractable iron content was roughly doubled. Correction for dissolved organic carbon (DOC) complexation with the speciation model WHAM reduced the difference in sorption between treatments, but the sludged soil still had significantly smaller Kd values (p < 0.01). Batch equilibrations without addition of Cd showed that there was no significant difference in the solubility of "native" cadmium (defined as EDTA-extractable Cd) in sludged and control soils. The reason for the lack of increase in Cd sorption in the sludge-amended soil has not been established, but it may be due to competition for sorption sites on humic compounds with sludge-derived Fe and trace metals such as zinc. The fact that the pyrophosphate-extractable (i.e., organically associated) iron content was seven times larger in the sludged soil provides some supporting evidence for this hypothesis.

Relationship between organic matter humification and bioavailability of sludge-borne copper and cadmium during long-term sludge amendment to soil

“…Accordingly, there are two theories regarding this regulation. One is known as the 'time-bomb' viewpoint, which indicates that the change in bioavailability of heavy metals in sludge accounted for the bondability of organic matter to different heavy metal fractions (Bergkvist et al, 2005;McBride, 2003;Stietiya and Wang, 2011). In this theory, the proportion of active fractions of heavy metal increases after sludge is recycled to soil as the sludge is gradually degraded.…”

“…5). There is a consensus that the proportion of Cd in the active fraction remains constant during long-term reuse of composted sludge by application to soil (Bergkvist et al, 2005;Tapia et al, 2010), indicating that the pitch point of regulation for active Cd is not dependent on the change of humus in sludge-amended soil, at least in composted sludge. There are two possible reasons for why active Cd did not vary.…”

Kinetics of cadmium adsorption on aluminum precipitation products formed under the influence of tannate

“…Cadmium (Cd) being more weakly bound to soil constituents compared to other trace metals is recognized as one of the most mobile trace metals circulating in the environment; it can readily enter the human food chain (McLaughlin and Singh, 1999;Kabata-Pendias, 2000;Adriano, 2001;Noonan et al, 2002;Satarug et al, 2003;Adams et al, 2004;Bergkvist et al, 2005;Krishnamurti et al, 2005). Its toxicity threatens human and animal health by causing kidney and liver dysfunction, weakening immune system, and adversely affecting reproduction (Chaney et al, 1999;Satarug et al, 2000).…”

Fissure and mineral weathering impacts on heavy metal distribution in sludge-amended soil

“…This downward mobility has been documented widely and several contributing factors are now recognized: firstly the existence of preferential percolate flowpaths within the soils; and secondly the chemical interaction of trace metals with the soil components through complex formation with organic matter and dissolved organic carbon (DOC) (Christensen et al 1996;McBride et al 1999), sorption on clay minerals and/ or Mn, Al, and Fe oxides or hydroxides, precipitation or dissolution of metallic coumpounds in contact with soil solutions (Bergkvist et al 2005). It shoud be noted that the total carbon contents in the amended and control soils are similar and very low, decreasing from 1.82% to 1.95% in the A horizon to 0.85-0.63% in the Bw horizon and zero in the C horizon, i.e., at 120 cm depth (Fig.…”