Effects of Sludge and pH Adjustment on Cd Speciation in Soil and Growth and Cd Accumulation in Pak Choi

Abstract

The objective of this study was to assess the effects of soil pH adjustment and treatment with sludge on plant growth and cadmium (Cd) accumulation in Chinese cabbage (pak choi) grown in Cd-contaminated soils. Soil was artificially spiked to raise its final Cd concentration to 10 mg/kg, adjusted to different pH values, and then supplemented with 5% sludge: either biosolids (BS) from wastewater treatment or sludge from drinking water treatment (WTS). Pak choi seeds were sown and the seedlings potted in the treated soil, then grown in a greenhouse for 45 days. The added Cd was present mainly in the exchangeable fraction and its concentration correlated to Cd accumulation in the roots and shoots. Adjustment of pH and application of sludge affected the Cd concentration in different fractions. Addition of WTS and adjustment to pH 7.0 inhibited growth and Cd accumulation in the pak choi. Addition of BS increased the soil nutrient content and thus enhanced growth and Cd accumulation. If pak choi were the only form of vegetable intake, consumption of pak choi grown in the Cd-spiked soils used in this study would exceed the maximum acceptable intake (60 mu g/day) proposed by the World Health Organization

Phytoremediation

“…Relative to control without applying BS, the Cd concentrations in the edible parts of pak choi grown in the Cd-contaminated soils amended with BS also increased (Lu et al 2012). Experimental results of forgoing studies show that BS can promote both the biomass and the accumulation of Cd which may decline the period needed in phytoextraction.…”

“…According to US Environmental Protection Agency in 40 CFR Part 503, biosolids (BS) are defined as sewage sludge that is beneficially reused (US EPA 2000) and could raise the dry weight (DW) of soybeans (Vieira 2001) and pak choi (Lu et al 2012). Relative to control without applying BS, the Cd concentrations in the edible parts of pak choi grown in the Cd-contaminated soils amended with BS also increased (Lu et al 2012).…”

Effect of Modified Illite on Cd Immobilization and Fertility Enhancement of Acidic Soils

“…Numerous studies have shown that pH greatly affects the bioavailability of Cd, such that the effectiveness of Cd in the soil is higher when the pH is lower, thus intensifying its damage to crops [58,59]. Natural illite contains many alkaline earth metals, such as potassium.…”