Assume that Peoria\'s drinking water supply contains polychlorinated biphenyls (

Question

Assume that Peoria's drinking water supply contains polychlorinated biphenyls (PCBs) which are chemicals that can disrupt the endocrine system of humans, cause liver damage, and are carcinogenic. Based on exposure assessment and using properly cited values of population, potency (or slope) factor, and the maximum contaminant level, MCL, (mg/L) for PCBs established by the US Environmental Protection Agency (EPA), estimate the: (a) chronic daily intake (mg/kg-day) of PCB by an adult male who consumes one gallon of city water each day and is away from the city a total of two months each year. (b) upper-bound cancer risk per person (c) number of additional cancer cases per year to expect in the entire population

Explanation / Answer

The population of Peoria as per 2016 is 1,14,265 . The maximum contaminant level for PCBs as described by EPA is 0.0005 (mg/lt)2

(a). Now if a person drinks 1 gallon(3.785 lt) of water each day then the amount of chronic PCB intake will be

Intake = 3.785 × 0.0005

= 0.00189

(b). Cancer slope factors (CSF) are used to estimate the risk of cancer associated with exposure to a carcinogenic or potentially carcinogenic substance. A slope factor is an upper bound, approximating a 95% confidence limit, on the increased cancer risk from a lifetime exposure to an agent by ingestion or inhalation. This estimate, usually expressed in units of proportion (of a population) affected per mg of substance/kg body weight-day, is generally reserved for use in the low-dose region of the dose-response relationship, that is, for exposures corresponding to risks less than 1 in 100.

For each age interval "i", the cancer risk for exposure by a specified pathway is computed as:

Riski = ( C × IRi × EFi × EDi × SF × ADAFi )/ BWi × AT

Where:

C = Concentration of the chemical in the contaminated environmental medium (soil or water) to which the person is exposed. The units are mg/kg for soil and mg/l for water.

IRi = Intake rate of the contaminated environmental medium for age bin "i". The units are mg/day for soil and l/day for water.

BWi = Body weight of the exposed person for age bin "i".( Let us consider the person is 70 kg)

EFi = Exposure frequency for age bin "i" (days/year). This describes how often a person is exposed to the contaminated medium over the course of a typical year. As the person is out from city for 2 months so total days will be (365-61) = 304 days

EDi = Exposure duration for age bin "i" (years). This describes how long a person is exposed to the contaminated medium over the course of their lifetime. (Let us consider that the person is exposed from 35 yrs of age)

AT = Average days. This term specifies the length of time over which the average dose is calculated. For quantifying cancer risk a "lifetime" of 70 years is used (ie, 70 years times 365 days/year).

SF = Cancer slope factor (mg/kg-day)1 In case of PCB it is (2 mg/kg-day)-1

ADAF = Age-dependant adjustment factor for age bin "i" (unitless) ( As we have assumed the person to be 35 yrs of age his ADAF will be 1)

Risk =( 0.0005 x 0.00189 x 304 × 35 x 2 x 1)/70 x 70

= 4.1 × 10-6

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