Step 5: Risk Characterisation
If a 70-kg person consumes 2L of water per day and the water contains 50 ug/L of inorganic arsenic dissolved, then the person's mg/kg/day intake is: 0.05 * 2/ 70 = 0.0014 mg/Kg/day
If we multiply this with 1.5, the cancer slop factor, we get = 0.0021 or 21 per 10, 000. Thus the risk of skin cancer (squamous cell carcinoma of skin resulting from skin lesions attributed to inorganic arsenic through oral consumption) is high if a person continues to consume water contaminated with inorganic arsenic.
Challenge for you:
What is the lifetime risk of cancer for a person who consumes 2L of water (assume 70 kg weight) but where the water arsenic concentration is 100 ug/L
Risk Mitigation
As the risk of skin diseases is very high with this level of exposure to inorganic arsenic, steps must be taken to reduce inorganic arsenic in the drinking water supply. This can be done through technological manipulation so that arsenic is removed from water at the source, or through legislature by prohibiting the people in the region to consume water, or through behavioural modification where the administration can take steps to make people consume safer water.
Case 3: Risk assessment of chlorination of drinking water of Christchurch
Step 1: Issue identification
Recently, as the Christchurch city council decided to add chlorine to the water supply, several members of the public raised concerns about health issues. Some complained that they suffered from eczema or dryness of skin, others complained that high chlorine content of water might trigger asthma and breathlessness among children. Yet others raised concerns about their pet fish dying in the tank. High chlorine content of water alters the pH of the water supply, as a result, the City council issued advisories about using filters for those patients who underwent dialysis, or those who had aquarium where they could use filters to control excess chlorine to protect against fish death. Here, we are concerned about health effects of humans.
Step 2: Hazard Identification
According to Villanueva (2015), there is some evidence that disinfection by-products are associated with health effects including respiratory effects in children, dryness of skin, reproductive effects related to spermatogenesis; however a comprehensive review failed to identify unequivocally major carcinogenic health effects \cite{Villanueva_2015}. They also concluded that
In summary, despite a large body of research, there is no clear evidence linking exposure to DBPs and reproductive outcomes, with the exception of a slight association with fetal growth-related outcomes and sporadic associations with some categories of congenital anomalies