Soil threshold values of total and available cadmium for vegetable growing based on field data in Guangdong province, South China

Abstract

Cadmium-contaminated risk for vegetable production in Guangdong province might have been over-estimated according to the Chinese Environmental Quality Standard for Soil.

Derivation of soil Pb/Cd/As thresholds for safety of vegetable planting: A case study for pakchoi in Guangdong Province, China

“…The heavy metal uptake of vegetables in the artificial addition experiment with heavy metal salt solutions is usually expected to be higher than that in the field situation (Alexander et al 2006;Yang et al 2009;Zhang et al 2010). Based on the field samples of three leafy vegetable species, Sun et al (2013) determined the soil threshold values of total Cd and available Cd (2.42 and 1.08 mg kg -1 , respectively) for leafy vegetables in Guangdong Province. A case study on safe limit of the soil As from West Bengal also suggested that the permissible limit of Olsen-extractable As and total As in soil for rice cultivation were varied according to the soil pH and organic carbon contents in different regions (Golui et al 2017).…”

“…The geographic coordinates of Guangdong Province is 20°10´-25°31´N and 109°41´-117°17´E which represents an area of 1.78×10 5 km 2 in South China. The whole area is characterized by a sub-tropical monsoon climate with mean annual precipitation of 1 336 mm and mean annual air temperature of 21.1°C (Sun et al 2013). The typical soil profile is Al-enriched weathering profile developed on a variety of rocks, such as granite, sand shale, limestone and basalt, with granite as the most extensive parent rock (occupying more than 40% of the Guangdong area) .…”

“…The topsoil sub-sample was taken for each one of the five sub-samples of vegetables and then mixed thoroughly as a bulk sample at each vegetable-sampling site. The collected vegetable and soil samples were stored in sealed polyethylene plastic bags and brought back to the laboratory as soon as possible (Sun et al 2013).…”

“…The total soil As concentrations were determined using a cold-vapor atomic fluorescence spectrometry (CVAFS) (Chen and Zheng 2000). The soil available Pb and Cd concentration (<2 mm soil) was extracted with a solution of 0.005 mol L −1 DTPA+0.01 mol L −1 CaCl 2 +0.1 mol L −1 triethanolamine and then measured by GFAAS (Sun et al 2013). The soil available As concentration was extracted with 0.5 mol L −1 NaH 2 PO 4 and then measured by CVAFS (Huang et al 2006).…”

“…However, more and more investigations revealed that the exceeding standard rates of heavy metals in soil were often inconsistent with those in vegetables from the same producing areas (Cui et al 2012;Sun et al 2013), which suggested that the current soil quality standards could not truly reflect the needs of ensuring the quality and safety of vegetables. This phenomenon was mainly due to the fact that the different soil physical and chemical properties would influence soil heavy metal bioavailability (Moreno et al 2009;Pietrzykowski et al 2014), and different species or cultivars of vegetables were diverse in the absorption capacity of heavy metals (Yang et al 2009(Yang et al , 2011Meng et al 2016).…”