2.2. Non-carcinogenic health-risk assessment

To estimate the non-carcinogenic risk of heavy metal ingestion resulting from protein powder supplement consumption, a hazard quotient (HQ) for 3 of the 4 metals (As, Cd, and Hg) was determined using the standard US EPA methodology [18]. The EPA reference doses (RfDs) for inorganic As, Cd, and the screening level for Hg are 3 × 10⁻⁴ mg/kg/day (0.3 μg/kg/day), 5 × 10⁻⁴ mg/kg/day (0.5 μg/kg/day), and 3 × 10⁻⁴ mg/kg/day (0.3 μg/kg/day), respectively [18, 45]. The RfD is an estimate of a daily oral exposure to the human population (including sensitive subgroups) that is likely to produce no appreciable risk of deleterious effects during a lifetime [44]. In this analysis, it was assumed that a 70 kg adult ingested the protein powder supplements. The following equation was used to calculate the HQ:

The cumulative risk of the evaluated heavy metals was expressed as a hazard index (HI), which is the sum of the HQs for As, Cd, and Hg [18].

Since there is no RfD for Pb, it was not included in the HQ analysis. However, we characterized the risk of Pb exposure via changes in blood lead levels (BLLs). The EPA adult lead model (ALM) was selected to estimate adult BLLs, as the EPA recommended this model for assessments of non-residential Pb exposures that result in BLLs <25 μg/L [43]. A baseline adult BLL of 1.27 μg/dL was used, which was the calculated weighted geometric mean of BLLs in adults aged 20 years or older during the 2005–2012 NHANES survey years [40]. We assumed that individuals consumed 1 or 3 servings of protein powder per day, for a total of 365 days per year.

Gastrointestinal absorption of Pb was conservatively assumed to be 20 % [39,47]. The BLL guidance value of 5 μg/dL from the Center for Disease Control (CDC) was used as the benchmark in this analysis. Additionally, the change in BLL from baseline was calculated for each exposure scenario.