Heavy metal and soil nutrient accumulation and ecological risk assessment of vegetable fields in representative facilities in Shandong Province, China

Shandong is one of the main areas for protected vegetable cultivation in China. A total of 88.5% of the facility soil samples had a pH between 7.0 and 8.4, indicating the majority of the soils were alkaline. Key properties, including total nitrogen (TN), organic matter (OM), electrical conductivity (EC), available phosphorus (AP), and available potassium (AK), showed an increasing trend with the number of years. The geoaccumulation index (I_geo) indicated that the Cd and Hg contents ranged from uncontaminated to moderate contaminated, while the risk of Hg and Cd reached the class of considerable risk as indicated by the potential ecological risk factor ($E_r^i$). The mean of Hakanson potential ecological risk index (RI) was 234.00, with the highest contribution from Hg (55.26%), followed by Cd (38.81%). It indicated that the survey area was at the moderate-risk level and Hg had the highest potential ecological risk factor, followed by Cd.