From the above documentation, we know Rfd for inorganic arsenic causing Hyperpigmentation is 0.0003 mg/kg/day
Step 4: Exposure assessment
Water arsenic concentration in that state was between 50 - 100 ug/L
Step 5: Risk characterisation
Let's estimate it in two ways:
- How much water would a person who weighs 60 kg will have to drink every day for 10 years in order to reach or exceed 0.0003 mg/kg/day: this amount will lead to skin lesions
- At the present rate of consumption of 2L of water per day from which the inorganic arsenic is derived, what is the dosage and how does that dosage relate to the Rfd
Scenario 1: How much water would a person need to drink till arsenic-caused skin lesions to appear?
If each L of water contains 50 ug (0.05 mg) of Inorganic arsenic, and the weight of the person is 60 kg, then we have 0.0008 mg/kg of inorganic arsenic intake already. How much liters of water per day will this person drink in order to keep within the 0.0003 mg/kg/day limit? His water intake needs to be limited to 375 milliliters or less than 400 ml of water every day. This amount of water consumption is less than optimum with maintaining a healthy life.
Scenario 2: If a 60-kg person consumes 2L of water per day, how much is that dosage for Rfd?
If the water contains 0.05 mg/L of inorganic arsenic, then by consuming 2L of water per day, he has 0.10 mg of arsenic per day. In terms of body weight (60 kg), we have: 0.0016 mg/Kg/day. As the Rfd is 0.0003 mg/Kg/day, this amount of consumption is equivalent of ~ 5.3 times that of the Rfd.
Challenge for you:
What happens to the skin disease risk if the person is consuming water that contains 100 ug/L of arsenic (0.10 mg/L of arsenic)?
Risk characterisation for cancer
Here we will model for the cancer related health effects. Assuming an exposure level of 50 ug/L in water and assuming that the sole source of inorganic arsenic is from drinking water at the rate of 2L/day for a 70 kg man, what can we say about the cancer risks?
Step 3: Dose response effect