It is well understood that pollutants in the Environment can be in the form of solid, liquid or gas. Furthermore, these pollutants can be physical, chemical or biological. An excess of any of these forms of pollutants in the environmental causes widespread degradation and may have adverse effects on humans, livestock, flora & fauna.

A very important field of study of pollutants in the Environment is Toxicology. This article primarily focuses on Metal Toxicity and various case studies connected to it. But before we get on with heavy metal toxicity, there are some important terms that need to be highlighted.

  • Toxicants

Most of the people today normally consider toxicants to be the same as pollutants, which is not true at all! A toxicant is any toxic/poisonous substance made by humans or introduced into the environment by human activity. A similar term used in conjunction with toxicants is toxins, which are toxicants produced naturally by a living organism.

The biggest difference between a pollutant and a toxicant is that toxicants are poisonous. Not every pollutant released into the Environment is poisonous. In brief, we can state that “All toxicants are pollutants, but all pollutants are not toxicants”.

Toxicants include environmental agents and chemical compounds found in nature, as well as pharmaceutical compounds that are synthesized for medical use by humans. These substances may produce toxic effects in living organisms including disturbance in growth patterns, discomfort, disease, and death.

  • Toxicology

Toxicology in simplest words is the scientific study of adverse effects that occur in living organisms due to chemicals. It involves observing and reporting symptoms, mechanisms, detection, and treatments of toxic substances, in particular, relation to the poisoning of humans.

  • Toxicity

Toxicity refers to the ability of a substance to produce adverse effects. These adverse effects may range from slight symptoms such as headaches to severe symptoms of coma, convulsions, or death. Poisons work by altering normal body functions. Most toxic effects are naturally reversible and do not cause permanent damage if prompt medical treatment is sought. Some poisons, however, cause irreversible (permanent) damage.

Metal Toxicity

Metal Toxicity

Metal Toxicity or Metal Poisoning is increasingly being recognized as dramatic in large parts of the developing world, particularly in India and China. Contamination of dietary substances by chemicals and non-essential elements such as heavy metals is known to have a series of adverse effects on the body of humans and animals. Because they are ubiquitous and recalcitrant, their entry into the body poses a potential health risk to human populations.

Metals can escape control mechanisms such as homeostasis, transport, compartmentalization, and binding to specified cell constituents, thus they can have toxic and even lethal effects. Heavy metals can cause malfunctioning of the cellular processes via displacement of essential metals from their respective sites. Oxidative deterioration of biological macromolecules has been found to be primarily due to binding of metals to DNA and nuclear proteins.

Symptoms are often the first indicators of contamination, and as such help to identify the contaminant. Symptoms that arise as a result of metal poisoning include intellectual disability in children, dementia in adults, central nervous system disorders, kidney diseases, liver diseases, insomnia, emotional instability, depression and vision disturbances.

In short, toxicity associated with exposure to metals if unrecognized or inappropriately treated represents a clinically significant medical problem, having a greater impact on increasing the morbidity and mortality rate.

The most common metallic elements like Mercury, Arsenic, Cadmium, and Lead are able to induce toxicity even at lower levels of exposure are considered systemic toxicants, occupying the top position on the list of hazardous substances. Neurotoxic effects are mainly associated with the organic form of mercury following its accumulation in the motor regions of the brain and Central Nervous System (CNS).

In nature, the majority of MeHg is contributed by the action of microorganisms in an aquatic ecosystem through bio-methylation of inorganic mercury derived mainly from anthropogenic sources. Possessing an enormous potential to undergo Bio-magnification, its accumulation (Bio-accumulation) in fishes renders communities highly vulnerable to its toxicity.

Popular case studies

There have been numerous infamous cases of high scale metal toxicity that caused widespread damage to regional environments and also caused outbreaks of various metal poisoning diseases.

  • Minamata Disease

Minamata Disease

Minamata disease sometimes referred to as Chisso-Minamata disease, is a neurological syndrome caused by severe Mercury poisoning that occurred in Minamata, Japan in 1956. It is the first of the two Minamata outbreaks that occurred in Japan within a span of 9 years. A second outbreak of Minamata disease occurred in Niigata Prefecture in 1965, known as the Niigata Minamata disease

Cause and History

Minamata disease was first discovered in Minamata city in Kumamoto prefectureJapan, in 1956. It was caused by the release of Methylmercury in the industrial wastewater from the Chisso Corporation‘s chemical factory. The factory released large quantities of industrial wastewater that was contaminated with highly toxic methylmercury.

This highly toxic chemical bioaccumulated in shellfish and fish in Minamata Bay and the Shiranui Sea, which, when eaten by the local populace, resulted in mercury poisoning. While cat, dog, pig, and human deaths continued for 36 years, the government and company did little to prevent the pollution.


The critical target of this compound is the Central Nervous System. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, loss of peripheral vision, and damage to hearing and speech. In extreme cases, insanity, paralysis, coma, and death follow within weeks of the onset of symptoms. A congenital form of the disease can also affect fetuses in the womb.


As of March 2001, 2,265 victims had been officially recognized as having Minamata disease (1,784 of whom had died) and over 10,000 had received financial compensation from Chisso. By 2004, Chisso Corporation had paid $86 million in compensation, and in the same year was ordered to clean up its contamination.

  • Itai-Itai Disease’

Itai Itai Disease

Itai-Itai disease was the name given to the mass Cadmium poisoning of Toyama PrefectureJapan, starting around 1912. The term Itai-Itai “ is the Japanese translation for “Ouch-Ouch” and the name of the disease was coined by locals for the severe pains victims felt in the spine and joints.

Cause and History

Itai-Itai disease was caused by Cadmium poisoning due to mining in Toyama Prefecture. The earliest records of mining for gold in the area date back to 1710. Regular mining for silver started in 1589, and soon thereafter, mining for lead, copper, and zinc began. Increased demand for raw materials during the Russo-Japanese War and World War I, as well as new mining technologies from Europe, increased the output of the mines, putting the Kamioka Mines in Toyama among the world’s top mines. Production increased even more before World War II. Starting in 1910 and continuing through 1945, cadmium was released into rivers by mining companies in the mountains in significant quantities, and the disease first appeared around 1912.

Due to the cadmium poisoning, the fish in the river started to die, and the rice irrigated with river water did not grow well. The cadmium and other heavy metals accumulated at the bottom of the river and in the water of the river. This water was then used to irrigate the rice fields. The rice absorbed heavy metals, especially the cadmium. The cadmium accumulated in the people eating contaminated rice.


Cadmium poisoning mainly causes softening of the bones. Spinal and leg pain is common, and a waddling gait often develops due to bone deformities caused by the cadmium. The pain eventually becomes debilitating, with fractures becoming more common as the bone weakens. Other complications include coughing, anemia, and kidney failure, leading to death.


Investigations revealed that the Mitsui Mining and Smelting’s Kamioka Mining Station caused the cadmium pollution and that the worst-affected areas were 30 km downstream of the mine. The polluting mining companies were successfully sued for the damage.

The reduction of the levels of cadmium in the water supply reduced the number of new disease victims; no new victim has been recorded since 1946. While the victims with the worst symptoms came from Toyama prefecture, the government found victims in five other prefectures.

The mines are still in operation and cadmium pollution levels remain high, although improved nutrition and medical care have reduced the occurrence of Itai-Itai disease.