Long‐Term Changes in the Extractability and Bioavailability of Zinc and Cadmium after Sludge Application

Abstract

Changes in the extractability and uptake by crops of sludge metals in a long‐term field experiment, started in 1942, were measured to assess whether Zn and Cd are either fixed by the sludge/soil constituents or are released as the sludge organic matter (OM) decomposes. Total and 0.1 M CaCl2‐extractable concentrations of Zn and Cd in soil and total concentrations in crops were measured on archived crop and soil samples. Extractability of Zn as a proportion of the total ranged from 0.5 to 3% and that of Cd from 4 to 18%, and were higher in sludge‐amended than farmyard manure or fertilizer‐amended soils. Over a 23‐yr period after 1961, when sludge was last applied, the extractability of both metals fluctuated, but neither decreased or increased consistently. The relationships between total soil and crop metal concentrations were linear, with no evidence of a plateau across the range of soil metal concentrations achieved. The slopes of the soil‐plant relationships depended on the type of crop or crop part examined, but were generally in the order red beet (Beta vulgaris L.) > sugar beet (Beta vulgaris L.) > carrot (Daucus carota L.) > barley (Hordeum vulgare L.). However, there also were large seasonal differences in metal concentrations in the crops. It is concluded from the available evidence that up to 23 yr after sludge applications cease, Zn and Cd extractability and bioavailability do not decrease.

Study of potential impacts of using sewage sludge in the amendment of desert reclaimed soil on wheat and jews mallow plants

“…Also, sewage sludge used in this study compared to desert soil was found to have higher levels of N, P, and K than in desert soil, hence, the contents of these elements gradually increased as the ratio of sewage sludge increased in sewage sludge desert soil mixtures. The main problems of an excessive application of sewage sludge are plant toxicity due to the accumulation of heavy metals in soils (McGrath et al, 2000) but also the increase in its salt content (Hao and Chang, 2003). Sewage sludge metal contents could be arranged in the following order according to their contents; Zn > Cu > Pb > Cd.…”

Cadmium in soils and cereal grains after sewage-sludge application on French soils. A review

“…How much do the chemical forms in which these metals occur -and their carrier phases -change over time, when comparing newly spread sludge with 5-to 10 year-old residues (McGrath et al, 2000;Bergkvist et al, 2003)? Which constituents of the receiving soils, such as iron and manganese oxides, clay minerals and organic matter, will immobilise such metals?…”

Effect of biosolids application on soil chemical properties and uptake of some heavy metals by Cercis siliquastrum

“…Some authors also reported similar findings (Jordao et al, 2003;Karami et al, 2009 andMcGrath et al, 2000). One aspect which should be taken into account is that the addition of sludge not only results in an increase in the total concentrations of metals, but also in the quantity of organic matter, which may have a direct effect on their solubility and bioavailability (McBride et al, 1997).…”