Here's a breakdown of how it forms:

Natural processes:

* Microbial methylation: Microorganisms in soil, water, and sediment can convert inorganic mercury (Hg) into methylmercury (CH3Hg+), the most common form of organic mercury. This process is called methylation.

* Volcanic emissions: Volcanoes release mercury into the atmosphere, where it can be transformed into organic mercury through photochemical reactions.

Human activities:

* Industrial emissions: Burning fossil fuels, mining, and industrial processes release mercury into the environment.

* Waste disposal: Improper disposal of mercury-containing products (like batteries, thermometers, and fluorescent lights) can lead to the formation of organic mercury in landfills and wastewater.

* Agricultural practices: Mercury-containing pesticides and fungicides can be used in agriculture, which can contribute to the formation of organic mercury.

How it happens:

* Methylmercury formation: Microorganisms convert inorganic mercury into methylmercury by attaching a methyl group (CH3) to the mercury atom. This occurs in various environments, including water, soil, and sediment.

* Bioaccumulation: Methylmercury is highly lipid-soluble, which means it can easily accumulate in living organisms. This can lead to high concentrations of methylmercury in fish and other aquatic animals.

* Biomagnification: As predators consume prey, the concentration of methylmercury increases with each trophic level. This is known as biomagnification.

Key takeaway: Organic mercury is not a manufactured substance but rather a consequence of both natural processes and human activities that involve mercury. Its formation is a significant concern due to its toxicity and ability to accumulate in the food chain.