Understanding Inorganic Mercury: Sources and Detection

Inorganic mercury is a mercury subcategory that refers to specific mercury compounds, occurring when mercury combines with other elements. Inorganic mercury is created when metallic mercury binds with sulfur, chlorine, oxygen, or other elements to create salts. This compound can be found naturally in soil or rocks or released by industrial pollution.

Understanding inorganic mercury is immensely important as it serves as a building block and can lead to even more dangerous compound creation. In fact, many times after being released into the environment, inorganic mercury can be impacted by aquatic bacteria that then transforms it into methylmercury, a highly toxic form of mercury that can cause serious ecological and health risks.

Sources of inorganic mercury include exposure through the use of everyday products, which result from contaminated environments or being in specific occupational environments. Cosmetics, household products, and industry items like older disinfectants, batteries, and thermometers can all be sources.

Detection and testing methods for inorganic mercury include identifying the compound by separating it from other forms, like organic methylmercury, using specialized analytical equipment. Testing methods include human exposure testing, environmental sampling detection, and liquid chromatography.

Inorganic mercury includes a category of mercury compounds that are formed when mercury combines with elements other than carbon. Common forms include mercuric chloride (HgCl₂), mercurous chloride (Hg₂Cl₂), mercuric sulfide (HgS), mercuric acetate Hg(CH₃COO)₂, and mercuric oxide (HgO).

• Mercuric Chloride: Mercuric chloride is the most common form of inorganic mercury and looks like a white powder. It is highly soluble in water. 
• Mercurous Chloride: With an appearance of an insoluble white powder, this has been used for decades in products like worming medications, laxatives, and tooth powders. It has been largely eradicated but still shows up in some imported home remedies on occasion. 
• Mercuric Sulfide: This form of inorganic mercury is a naturally occurring mineral. It is less soluble when compared to other forms, like mercuric chloride, and is colored a bright red. 
• Mercuric Acetate: This highly toxic, white crystalline chemical compound is reactive and demands adherence to strict safety measures. It is fatal if swallowed, inhaled, or absorbed through the skin and can have long-lasting environmental consequences, especially on aquatic life. 
• Mercuric Oxide: Either red or yellow, this form of inorganic mercury is a crystalline powder. It has been used in years past in batteries and has also been used historically as a topical disinfectant or as a chemical catalyst.

The stability of inorganic mercury varies based on the surrounding matrix and the oxidation state. It can also be highly reactive, especially with sulfur along with other trace elements. Inorganic mercury is not as toxic or environmentally bioaccumulative when compared to organic mercury or methylmercury.

Inorganic mercury targets the kidneys and does not readily cross the blood-brain barrier or placental barriers, which is the way that organic mercury targets the body, leading to severe and permanent neurological damage. It’s also harder to be exposed to inorganic mercury as it is usually occupational exposure, with organic mercury being a risk for virtually anyone.

Overall, inorganic mercury finds its way into the environment through a mixture of human industrial activities and naturally occurring geological processes. This creates a perfect storm scenario that plays out across the globe, resulting in mercury being released from the air, water, soil, and even through specific commercial products. While natural sources have established a baseline of releasing mercury into the environment, human activities have increased the mercury currently circulating in the oceans and atmosphere, negatively impacting global ecosystems. 

Natural Sources

Natural sources include geological processes that can release mercury that has been locked away in the Earth’s crust. This can occur in any of the following ways.

• Volcanic Eruption: This is one of the most significant natural contributors to inorganic mercury release. Elemental mercury gas along with particulate inorganic mercury are released directly into the environment during an eruption. 
• Geothermal Activity: Deep-sea hydrothermal vents and hot springs release mercury-laden fluids into aquatic ecosystems. 
• Erosion and Weathering: The chemical and physical breakdown of rocks gradually releases inorganic mercury salts into surface water and soil. 
• Biomass Burning Combined With Oceans: Forest fires release mercury back into the atmosphere that has been previously absorbed. Ocean surfaces then absorb and re-emit mercury as an elemental vapor. 

Human or Anthropogenic Sources

Anthropogenic activities mobilize large amounts of mercury that would remain trapped underground and impact global atmospheric deposition. Human activities can be the source of mercury release in the following ways: 

• Ore Mining and Processes: This occurs due to two different fields, one that mines mercury for extraction (the primary source) and the other being artisanal, when mercury is used to amalgamate gold. These processes release vaporized elemental mercury into the air and leaves behind the inorganic mercury compound that then contaminates surrounding soil and mine waste. 
• Industrial Processes: Another human-initiated source of mercury release includes industrial release through metal smelting, cement manufacturing, and by chlor-alkali facilities that used mercury to produce caustic soda and chlorine. This releases inorganic mercury in large volumes into wastewater and the air.  
• Fossil Fuel Combustion: Burning of oil or coal for energy is the primary source of mercury emissions into the atmosphere. Coal contains trace amounts of mercury naturally, which is then released as inorganic vapor when burned. 
• Waste Incineration: Another common human-caused source of mercury release is waste incineration. Burning medical waste, municipal solid waste, and other hazardous materials releases mercury from within discarded products that contain mercury, like fluorescent lamps, batteries, and thermometers into the atmosphere.

It’s worth noting that, in addition to the sources listed above, inorganic mercury is still being used in some unregulated skin-lightening creams and cosmetic products, herbal home remedies, batteries, chemical wood preservatives, and antiseptic soaps, which present another avenue of exposure. 

Inorganic mercury primarily affects the digestive system and the kidneys since inorganic mercury compounds are water-soluble and highly corrosive. Ingesting inorganic mercury can lead to severe damage to the gastrointestinal system. Prolonged exposure overtime can lead to systemic toxicity, which can impact a person’s health by affecting the central nervous system and the kidneys. Specific health risks associated with inorganic mercury include: 

• Kidney Damage: This involves specific conditions like renal toxicity, which can cause renal tubular necrosis, acute or chronic kidney failure, and/or decreased kidney function. Over time, exposure can cause leakage of excess protein into the urine, which indicates kidney distress, known as proteinuria. 
• Gastrointestinal Toxicity: Acute damage can include severe abdominal pain, damage to the mucus membranes, and vomiting after ingesting inorganic mercury salts. Massive fluid and blood loss can also occur due to overdose and can lead to hypovolemic shock or even potential death. 
• Behavioral and Neurological Effects: Even though inorganic mercury doesn’t cross the blood-brain barrier, it can still cause neuromuscular changes like tremors, muscle weakness, mood swings, and memory loss. It can also rarely result in acrodynia, which is called the pink disease. This presents as red and peeling skin on the hands and feet, extreme irritability, and heavy sweating. It is most often seen in children. 

The most vulnerable people groups as it relates to inorganic mercury exposure and the negative health effects that can occur include children, pregnant women, and individuals who are consistently exposed as part of their regular occupational duties. 

The primary environmental danger of inorganic mercury is the way that it acts as a building block for methylmercury. When inorganic mercury is deposited in the water or soil (through one of the sources listed above), it is converted via bacteria into this highly toxic form of mercury, methylmercury. This bioaccumulates into the food chain, which can have many environmental consequences. 

Bioaccumulation is a significant issue that starts at the base of the food chain with single-cell algae and phytoplankton. Inorganic mercury is flushed out as waste by the small animals that consume them. The contaminated small animals or fish are eaten by larger ones who are then impacted. This continues up the food chain until it gets to apex predators at the top of the food chain, like otters, swordfish, and tuna. The primary way that humans are exposed to mercury then comes to fruition when they consume predatory fish or shellfish that by now has accumulated methylmercury. 

Other ways in which the environment is impacted include microbial and plant distribution. Localized concentrations of inorganic mercury can reduce the presence of aquatic microorganisms, impact the diversity of the soil, and interfere with fundamental processes that are key to plant life like nutrient uptake and plant photosynthesis. Therefore, although inorganic mercury might not be as harmful alone as other forms, it acts as a catalyst for the most harmful type of all, methylmercury, which then can be extremely devastating to an entire ecological system. 

There are many guidelines and regulations in place to protect the environment and the public in general from harm. This includes guidelines for mercury overall as well as inorganic mercury regulations. The Minamata Convention on Mercury is at the cornerstone of global efforts to restrict mercury across its entire lifecycle, from mining and industrial manufacturing to waste disposal and product use. This treaty is a legally binding UN treaty that was specifically designed to curb anthropogenic releases and emissions. Many of the set standards and regulations from other agencies, both globally and throughout the United States, are designed to limit the exposure route of mercury either through oral ingestion or airborne inhalation. Following is a breakdown of some of these regulations. 

• Occupational Safety and Health Administration (OSHA): Ensures legal airborne limits for both inorganic and elemental mercury for an 8-hour span of time. Limit: PEL of 0.1 mg/m3.
• National Institute for Occupational Safety and Health (NIOSH): This limit on airborne mercury is based on a 10-hour work shift and recommends a ceiling amount that should not be exceeded. Limit a ceiling of 0.1 mg/m3.
• American Conference of Governmental Industrial Hygienists (ACGIH): This limit is based on an 8-hour weighted average. Limit TLV of 0.025 mg/m3. 

Other regulations include limits on emissions and release controls as well as a move to eliminate mercury use in general in manufacturing. In the United States, the EPA handles transboundary mercury pollution through various statutes, including the Clean Air Act (CAA) as well as the Resource Conservation and Recovery Act (RCRA). 

There are several ways to detect the presence of mercury. Detection includes using spectroscopic methods, like CV-AAS, CV-AFS, and ICP-MS, along with electrochemical and biosensors and colorimetric and optical sensors, as well as urine and blood tests. In addition to avoiding contact with mercury salts, adhere to the following to best practices to reduce the risk of inorganic mercury exposure:

• Follow disposal guidelines, which include proper disposal of fluorescent tubes and CFLS. 
• Avoid certain creams that have inorganic mercury as an ingredient.
• Replace old household items like thermostats, thermometers, and barometers with digital alternatives.
• Practice proper cleanup procedures with mercury, never use a vacuum for cleanup, and follow EPA cleaning spill guidelines.
• Wear appropriate personal protective equipment when working around mercury, change work clothes and shoes before leaving the jobsite, wash face and hands, and shower immediately after finishing a shift. 

It’s important to understand prevention methods and regulatory guidelines that exist throughout various industries. At AGS Scientific, we can help with how to choose the right mercury analyzer for your needs. It takes a concerted effort across several industries to reduce mercury toxicity and to ensure safe food, water, and products. Contact us today to learn more about mercury detection and finding the right mercury analyzers.