Correlations between organophosphate flame retardants exposure and papillary thyroid cancer or thyroid hormones: A case-control study from Shijiazhuang, China

Organophosphate flame retardants (OPFRs), commonly used in consumer products to reduce fire hazards, have raised concerns due to their potential adverse health effects from environmental exposure. However, evidence linking OPFRs to specific health outcomes, including cancer, remains limited and inconclusive. This case-control study investigated the associations between OPFRs exposure, thyroid hormone levels, and papillary thyroid cancer (PTC) risk in 284 matched pairs of PTC patients and healthy controls from Hebei Province, China. Multiple analytical approaches-including multiple linear regression, restricted cubic spline regression, and conditional logistic regression-were employed to evaluate the relationships between individual OPFRs, thyroid hormone levels, and PTC risk. Additionally, Bayesian kernel machine regression (BKMR) model and Quantile g-computation models were utilized to further investigate the impact of OPFRs mixtures. Our results showed that OPFRs were detected in all plasma samples. Notably, a negative association was found between the exposure to Tri (2-butoxyethyl) phosphate (TBOEP) and the incidence of PTC (OR = 0.119, 95 % CI: 0.041, 0.349), though no overall link was found between OPFRs mixtures and PTC incidence. Moreover, in the case group, we showed a statistically significant positive association between OPFRs mixtures and triiodothyronine (T3) levels (β = 0.138, 95 % CI: 0.070, 0.207). Specifically, Tris(2-chloroethyl) phosphate (TCEP), Tris(2-chloro-1-methylethyl) ester (TCIPP), Tri-phenyl phosphate (TPHP), Tri-iso-butyl phosphate (TIBP), Tri-n-butyl phosphate (TNBP), and TBOEP showed significant positive correlations with T3 levels. In conclusion, there was no statistically significant association between OPFRs mixtures and PTC. In the case group, a positive relationship was found between OPFRs and T3 levels. It should be noted that we cannot establish a causal relationship between OPFRs and thyroid hormones based on this case-control study, and prospective studies are needed.