Which heavy metal has the most stringent regulations for land application?

Mercury has the most stringent regulations for land application due to its high toxicity and ability to bioaccumulate in the food chain. This heavy metal can have severe impacts on human health and the environment, leading to neurological and developmental issues. Consequently, regulatory agencies impose strict limits on its concentration in soils where land application occurs.

Mercury's persistent nature in the environment means that even small amounts can pose significant risks, especially in aquatic environments where it can convert to methylmercury, a highly toxic form that can accumulate in fish and other organisms. The careful regulation reflects an understanding of these environmental and health hazards, leading to more rigorous standards compared to other metals like lead, copper, and cadmium, which, while also regulated, do not have the same level of concern regarding their long-term environmental impact and human health risks when it comes to land application.