Dynamics of Cadmium Pollution Risk in Agricultural Land Soil of Tropical Islands in China from 2000 to 2024: A Case Study of Hainan Island

The issue of cadmium (Cd) contamination in agricultural soils has garnered significant attention due to its implications for food safety and environmental health. However, research on its spatial and temporal distribution in tropical agricultural zones with high intensity cropping remains limited. This study conducts a meta-analysis of 38 studies published between 2000 and 2024 to comprehensively assess Cd pollution on Hainan Island, China, a tropical region with three cropping cycles per year. By synthesizing 165 records from 4110 sampling sites, the analysis reveals that the mean Cd concentration stands at 0.12 mg/kg, with peak values reaching 3.11 mg/kg. Approximately 80.44% of sites fall into the categories of unpolluted or unpolluted to moderately unpolluted based on the geo-accumulation index, while 2.17% of sites exhibited heavy to extreme Cd accumulation, and 2.13% posed an high ecological risk (level IV). Spatially, Cd concentrations were lower in central areas, such as Baisha County, but higher in the northwest and southeast, notably in Haikou City in the northwest and Sanya City in the south. Over time, Cd pollution has intensified, with mean concentrations rising from 0.09 mg/kg (2005–2014) to 0.16 mg/kg (2017–2023), with exceedance rates rising from around 1% to between 7.78% and 20.93%, peaking in 2017. The increasing trend of cadmium accumulation is closely related to human activities, with agricultural, industrial, and transportation-related activities playing an increasingly significant role in Cd accumulation. Pesticide use, phosphate fertilizer application, and industrial emissions have been identified as major contributing factors. These findings highlight the need for targeted mitigation strategies to control pollution sources and ensure the long-term sustainability of agricultural production on Hainan Island.