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The two principal toxicity risk factors evaluated are the SF for carcinogen risk characterization and the reference dose (RfD) for non-carcinogen risk characterization (Li et al. 2013; Bamuwuwamye et al. 2017). The estimations of the magnitude, frequency, and duration of human exposure to each potentially toxic metal in the environment are reported as an ADD and it is calculated using the following equation:
formula
Here, ADDi (mg/kg/day) is the average daily dose through ingestion of water, Ci is the concentration of the metal (mg/L), IR is the ingestion rate, EF represents exposure frequency, ED is exposure duration, BW indicates body weight, AT is the average time for non-carcinogens, ET represents exposure time, and CF is the conversion factor (Wongsasuluk et al. 2016). Values of all the above parameters are presented in Table 2.
Table 2

Standard values for calculating exposure assessment of trace metals in waters (USEPA 1989; Demir et al. 2015)

IndexNameValueUnit
Ci Concentration of metal in water – mg/L 
IR Water ingestion rate L/day 
Ef Exposure frequency 365 Days/year 
Ed Exposure duration 70 Years 
Bwt Average body weight 70 kg 
At Averaging time 25,550 Days 
Cf Unit conversion factor 1 × 10−3 L/cm3 
RfDi Cd = 0.0005; Cr = 1.5; Cu = 0.037; Ni = 0.020; Pb = 0.036; Zn = 0.3; Mn = 0.14; Fe = 0.7   
IndexNameValueUnit
Ci Concentration of metal in water – mg/L 
IR Water ingestion rate L/day 
Ef Exposure frequency 365 Days/year 
Ed Exposure duration 70 Years 
Bwt Average body weight 70 kg 
At Averaging time 25,550 Days 
Cf Unit conversion factor 1 × 10−3 L/cm3 
RfDi Cd = 0.0005; Cr = 1.5; Cu = 0.037; Ni = 0.020; Pb = 0.036; Zn = 0.3; Mn = 0.14; Fe = 0.7   
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