Environmental pollution induced by heavy metal(loid)s from pig farming

The development of intensive and large-scale livestock farming, such as pig husbandry, is significantly increasing the amount of manure globally. Mineral additives are commonly used in animal feed, and heavy metal(loid)s (HMs) are introduced to the feed via incomplete purification processes of those mineral additives, which leads to inevitable environmental pollution by HMs in conjunction with manure production. When these toxic-metal-containing manures are used as fertilizer, the HMs accumulate in soils and crops, which further causes potential risks to human health and the ecological environment. In this review, the focus is on seven HMs that are related to human activities or frequently contained in animal feed, including copper, zinc, cadmium, chromium, lead, mercury, and arsenic. The toxicities of these HMs and the elimination methods to reduce the HM toxicity of pig manure when it is added to soil, i.e., liquid-solid separation, adsorption, bioleaching, and composting, are summarized. The ultimate aim of this review is to outline the systematic pollution management strategies for HMs from pig farming.