Lead, an essential part of water quality monitoring

Heavy metals usually refer to metals with a physical density greater than 4.5g/cm³, mainly distributed in subgroups of the periodic table, such as lead, copper, chromium, zinc, nickel, cobalt, and transition metal elements such as silicon, arsenic, and selenium. These elements are generally difficult to degrade and have biological toxicity, and are easy to accumulate under the action of the food chain and cause harm to the environment and human body. Lead (Pb) has special chemical properties and is a sticky metal. It has a high electronegative property and is easy to form a stable chemical structure with iron, aluminum, manganese oxides and organic matter. Therefore, it exists in many forms in the soil. The toxicity of lead depends primarily on the form and secondarily on the concentration. The form of lead in soil can be divided into exchangeable state, oxidizable state, reducible state and residue state. Among them, the exchangeable state has the strongest biological effectiveness, and the residue state is the least easily absorbed by organisms. Secondly, the physical and chemical conditions of the soil will affect the transformation of the form of lead, such as pH value, aeration and flooding conditions, humus content, etc. can all affect the form of lead, among which pH is one of the important factors determining the lead in soil solution, when pH When changing from low to neutral, the organic lead content in the solution increases sharply. Lead has long been defined by the WHO as an extremely toxic environmental and neurotoxic substance. Dietary accumulation or long-term exposure to lead-containing environments can damage a person's nervous, digestive, hematopoietic, and reproductive systems. The sources of lead in the environment are mainly divided into two types: natural sources and anthropogenic sources, mainly anthropogenic. Lead, which exists naturally in the earth's crust, can be released into the environment along with natural phenomena such as volcanic fly ash, ground dust, forest fire smoke and dust. Man-made activities are closely related to people's activities and production. In cities, domestic garbage landfills and industrial waste dumps directly lead to lead pollution and enter the human body through groundwater and food. In farmland, sewage irrigation is a major source of lead pollution. Due to the scarcity of fresh water resources, some areas have to use sewage irrigation to alleviate the water shortage. Since lead is not degradable, long-term irrigation with lead-containing sewage will inevitably lead to lead accumulation. For the remediation of heavy metal-contaminated soil, physical methods, chemical methods and biological methods are generally used. For the treatment of lead-contaminated soil, physical methods are divided into soil replacement method, thermal desorption method and vitrification technology. Chemical methods are divided into chemical rinsing, electrodynamic repair and stabilization repair. Biological methods are divided into phytoremediation and microbial remediation