## 2 Environmental and Human Health Impacts of Short-Chain Chlorinated Paraffins
Toddlers' high hand-to-mouth and object-to-mouth activity may contribute to the intake through food. Combined dust and food exposure also elevate the risk for occupational workers [54]. Therefore, to conduct a robust risk assessment of SCCPs, it is imperative to quantify the overall human exposure. This involves integrating exposure data from diverse sources, including consumer products, food items, and house dust. Furthermore, the potential co-exposure to POPs unintentionally present in SCCPs must be considered in both exposure and toxicity evaluations [13]. A risk assessment of SCCPs has been performed by several international and national organizations [55]. A tolerable daily intake (TDI) was proposed by the World Health Organization/International Programme on Chemical Safety (WHO/IPCS) and the UK Committee on Toxicity (UK-COT). The WHO/IPCS reviewedavailable data on the effects of SCCPs on human health and the environment in 1996 and established a tolerable daily intake (TDI) of 100 \(\mathrm{\mu}\)g/kg body weight (bw) per day for non-neoplastic effects. For neoplastic effects, it was recommended that daily doses of SCCPs for the general population should not exceed 11 \(\mathrm{\mu}\)g/kg bw per day. The UK-COT established a TDI of 30 \(\mathrm{\mu}\)g/kg bw per day. [PERSON] and [PERSON] recently compiled knowledge on the disposition of SCCPs in humans [56]. The data indicate that they can be efficiently absorbed from the gastrointestinal tract and lungs and subsequently distributed to various organs. However, research on the human body burden of SCCPs is limited [57]. So far, SCCPs have been detected in the brain, liver, kidneys, adipose tissue, blood plasma, blood serum, maternal/cord blood serum, placenta, breast milk, hair, and nails. Most studies have measured the SCCP concentration in blood, with significant differences being observed: from not detected (ND) to 72,449 ng/g lw [57]. The SCCP content in the next most studied matrix, breast milk, also varies significantly: from ND to 16,100 ng/g lw detected in milk samples from Chinese provinces [58]. The median concentrations of SCCPs detected were 681 and 733 ng/g lipid in 2007 and 2011, and variations of more than two orders of magnitude in CP exposure levels were found [58]. All reported placental samples contained SCCPs, and the highest value reported was 132 ng/g ww [57]. Most studies have documented the body burden of SCCPs in the Chinese population, which is higher than in other studied countries and regions, high-income countries from the northern hemisphere. There is a need for more research from other geographical regions with diverse populations to gain a deeper insight into the accumulation of SCCPs in the human body on a global scale. Furthermore, additional studies with larger sample sizes and a variety of ethnic groups are needed to enhance our understanding of possible threats to the fetus during pregnancy. Namely, the transfer of SCCPs from mother to fetus, partially restricted by a placental barrier, has been suggested based on higher concentrations in maternal blood in comparison to cord blood. The suitability of using hair and nails as indicators of human exposure has been assessed by [PERSON] et al. [59] While the homolog profiles of SCCPs in hair and nails were similar, the concentrations found in hair were markedly higher than those in nails. Age appears to be the main driver of SCCP accumulation in hair and nails, according to analysis. Given that hair and nail CP levels reflect both internal and external exposures, additional research is proposed to investigate the occurrence, partitioning, and transfer of SCCPs via paired blood and dust samples. The elimination of the SCCPs appears to be biphasic, with an initial rapid phase followed by a slower terminal phase, potentially involving long-term storage in fatty tissues [56]. SCCPs are primarily metabolized in the liver and excreted via bile and feces. The metabolic pathways of SCCPs are poorly understood, and no comprehensive metabolic scheme has been established.