Toxic Heavy Metals and Hazardous Waste: Health & Environmental Risks

Understanding Heavy Metal Toxicity

Heavy metals are naturally occurring elements that can become toxic at high concentrations. They pose significant health and environmental risks due to their persistence and ability to accumulate in biological systems.

Iron (Fe): Essential Nutrient, Potential Toxin

Iron (Fe) is an essential mineral, with daily requirements ranging from 10 to 18 mg. It is commonly found in meat, vegetables, and lentils. While vital for health, an iron overdose can cause symptoms such as vomiting and diarrhea.

Heavy metals, in general, are known to inactivate enzymes. In cases like mercury poisoning, enzymes crucial for catalyzing reactions linked to receptor molecules are affected, leading to the alteration and deformation of their active sites.

Specific Poisonous Heavy Metals

Mercury (Hg) Toxicity

Mercury (Hg) vapor is extremely toxic. An open container of mercury or a spill on the floor can release enough vapor to cause poisoning. Mercury has a cumulative effect; the body takes approximately 70 days to eliminate half of a given dose. Chronic poisoning results from continuous exposure.

Mercury is particularly dangerous for those who work with it, such as dentists who use it in dental amalgams. While antidotes exist, prevention is key. Mercury vapor is significantly more toxic than liquid mercury.

Symptoms of mercury poisoning include:

• Loss of balance
• Vision impairment
• Reduced sense of touch
• Hearing loss

Note: Arsenic-containing gases can also be deadly, inactivating enzymes by forming complex ions.

Lead (Pb) Poisoning

Lead (Pb) is a pervasive heavy metal. Many foods contain up to 0.3 ppm of lead. Drinking water can also contain lead, often up to 0.1 ppm, primarily from old pipes. Leaded gasoline, once a significant source of exposure, is no longer used.

In the body, metallic lead transforms into Pb+2 ions. Up to 2 mg of lead can be excreted per day. While the amount of lead absorbed from air, water, and food is generally much lower and rarely accumulates to toxic levels in adults, it is highly harmful to children.

Children, especially those living in older buildings with lead paint or in environments with poor lead safety practices, are particularly vulnerable. Lead exposure in children can cause mental retardation and neurological disorders.

Cadmium (Cd) Toxicity

Cadmium (Cd) is used less frequently than lead (Pb) and mercury (Hg). It is primarily utilized in alloys for the electronics industry and in rechargeable nickel-cadmium batteries.

Cadmium poisoning can lead to:

• Loss of calcium (Ca) from bones, making them brittle
• Abdominal pain
• Vomiting
• Diarrhea
• Asphyxia

Cadmium also significantly impacts the nervous system by disrupting the action of acetylcholine, a vital neurotransmitter. This interference with message transmission to receptors can result in paralysis, severe respiratory problems, or even death.

Hazardous Waste Management

Hazardous waste is defined as any waste that can cause or contribute to diseases, threaten human health, or harm the environment.

Classification of Hazardous Waste

Reactive Waste

Reactive wastes are those that react with water (H2O) and air. They can produce toxic gases such as hydrogen cyanide and hydrogen sulfide.

Combustible Waste

Combustible wastes are materials that can easily ignite and burn. Hexane is an example of a combustible hydrocarbon solvent.

Toxic Waste

Toxic wastes are substances that can cause harm when ingested, inhaled, or absorbed through the skin. For example, PCBs (polychlorinated biphenyls), often found in old transformers, are classified as toxic waste due to their carcinogenic properties.

Corrosive Waste

Corrosive wastes are highly acidic or alkaline substances that can dissolve or corrode other materials. Acids, for instance, cannot be stored in steel drums because they can corrode them. These wastes can often be neutralized with lime and safely disposed of with water.