In 2006, an apartment complex that included a playground was built on a piece of land that was the site of a metal processing plant that operated between 1930’s and 1950’s before going out of business. Due the above reason, the land had to be assessed for any carcinogenic heavy metals. There are so many potential heavy metals that could have hazardous effects on people’s health, but the assessment mainly focused on cadmium. This is because cadmium was the most common metal used in the plant while it was operational and the metal has both carcinogenic and non-carcinogenic endpoints.
The background cadmium in the area was found to be 500 mg/kg with the maximum cadmium concentration in 20 soil samples found to be 2000 mg/kg. These numbers were very high and could have adverse health effects on people living in the area considering soil cadmium concentrations in areas not contaminated by human activities ranges from 0.006 to 1.1 mg/kg (Lowe).
Health Effects of Cadmium
The only exposure routes of cadmium are inhalation and oral, no cadmium enters the body through dermal contact. About 5% to 50% of inhaled cadmium enters the body through the lungs where it is mixed with blood and transported to other parts of the body (World Health Organization). High inhalation exposures may result to acute pneumonitis or pulmonary oedema that are both lethal. There is sufficient evidence to show that long-term cadmium inhalation is associated with chronic obstructive airway disease that leads to lung cancer. Due to this carcinogenicity in humans, the International Agency for Research on Cancer has classified cadmium and its compounds as Group 1 human carcinogens. The cadmium inhalation Minimal Risk Levels (MRL) developed by the Agency for Toxic Substances and Diseases Registry are 3 ×10-5 mg/m3 for an acute-duration of fewer than 14 days and 1 × 10-5 mg/m3 for a chronic-duration of more than one year (Lowe).
Oral exposure to cadmium is mostly through ingestion of food and water containing cadmium. Cadmium binds to organic matter on the top soil and where it remains immobile until taken up by plants. Animals that also eat the plants may have high cadmium accumulations in their bodies. Cadmium also exists as hydrated ions with other organic and inorganic substances that are soluble in water. As such, cadmium can migrate and contaminate nearby water sources with high cadmium levels seen in most water sources in the vicinity of cadmium industries. If there is any aquatic life in the water, they will also accumulate the cadmium.
The plants, animals and aquatic life are all part of food supply and are consumed by humans. Only a small amount of cadmium of about 1% to 10% is absorbed into the body through the digestive tract (World Health Organization). Having insufficient iron in diets causes the body to absorb more cadmium than usual. The most affected parts of the body due to cadmium ingestion are the kidneys and the bones. When cadmium is absorbed into the body, it is first transported to the liver via the blood where it forms complexes by bonding to proteins. The complexes then move to the kidneys where they accumulate; the biological half-life of cadmium in humans is between 10 to 35 years (World Health Organization). This cadmium accumulation causes renal tubular dysfunction and glomerular damage resulting in increased excretion of essential proteins and sugars in the urine that is irreversible causing further kidney damage.
The MRL for cadmium ingestion is 1 ×10-5 mg/kg/day for a chronic-duration for more than one year (Lowe). Long-term consumption of cadmium results to disturbances in calcium metabolisms. This may lead to softening of bones and osteoporosis in those living in areas that are contaminated by cadmium. This was seen in Japan where a disease known as Itai-itai whose symptoms include painful bone fractures, kidney dysfunction, osteoporosis, and osteomalacia was observed in people living in an area with soil contaminated by cadmium.
Cancer Risk Calculation
Soil is the only hazard in the case hence the risk of cancer will be calculated due to accidental ingestion of contaminated soil.
Dosesoil ingestion = (Cs×IRs×AFGIT×Dhours×Ddays×Dweeks×Dyears)/RW×16× 365×L.E
Cs is the concentration of Cadmium in soil in mg/kg
IRs is the accidental soil ingestion rate in kg/day
AFGIT is the absorption factor by the gastrointestinal tract
Dhours is hours per day with exposure
Ddays is exposure days in a week
Dweeks is exposure weeks in a year
Dyears number of years of exposure
BW is receptor body weight in kgs
LE is life expectancy
Dosesoil ingestion = (500×0.00002×1×12×7×52×10×32.9×78.74)/32.9×16×365×78.74
H.I = sum of all H.Q
H.Q = Estimated dose/Tolerable daily intake = (0.28872× 10-5)/ (1.0×10-5)
Since soil is the only hazard in this case, then H.Q is equal to H.I that is 0.28872
Cadmium can only be released into the atmosphere during mining or smelting. The metal processing plant is no longer operational hence there is no cadmium in the air and therefore the residents of the apartment complex are not at any risk of inhaling cadmium and getting cancer. However, the residents are at risk of suffering from kidney dysfunction and bone related diseases due to ingestion of contaminated food. As such, people living in the complex should be discouraged from growing any food in the area or buying locally grown food. Children playing in the playground in the complex should also do so under strict supervision from adults. The children should not be let to put anything from the playground in their mouths. High hygiene standards should also be maintained while preparing food and before eating to prevent any accidental ingestion of cadmium. Phytoextraction should also be adopted as a gradual way of cleaning up the soils. The process involves slightly raising the acidity levels of the soils and growing a plant known as alpine pennycress in the soils. The plants thrive in soils contaminated with cadmium and absorb the metal from the soils thus cleaning them up. Annual harvesting of the plants makes it possible to reduce cadmium concentrations to normal levels in about three to ten years (Durham). The above-mentioned measures will mitigate any effects that cadmium might have on the residents of the apartment complex.
Durham, Sharon. “Using Plants to Clean up Soil.” United States Department of Agriculture. 2007. Web. 19 May 2016.
Lowe, Lisa. ToxGuide for Cadmium. N.p.: Agency for Toxic Substances and Disease Registry, 2012. Web. 19 May 2016.
World Health Organization. Exposure to Cadmium a Major Public Concern. N.p.: World Health Organization, 2011. Web. 19 May 2016.