Persistent halogenated organic pollutants (HOPs) are a class of toxic chemicals, which may have adverse effects on fetuses via transplacental transfer from their mothers. Here, we review reported internal exposure levels of various HOPs (organochlorinated pesticides, polychlorinated biphenyls, polybrominated diphenyl ethers, short- and medium-chain chlorinated paraffins, and per- and poly-fluoroalkyl substances) in placenta, and both maternal and umbilical cord sera. We also present analyses of the transplacental transfer and placental distribution characteristics of each class of compounds, and discuss effects of several factors on the transfer and accumulation efficiencies of HOPs, as well as the main mechanisms of HOPs’ transfer across the placental barrier. Reported compound-specific transplacental transfer efficiencies and distribution efficiencies, expressed as umbilical cord:maternal serum and placental:maternal serum concentration ratios (R_CM and R_PM, respectively), are summarized. Average published R_CM values of the HOPs range from 0.24 to 3.08 (lipid-adjusted) and from 0.04 to 3.1 (based on wet weights), and are highest for perfluoroalkylcarboxylates (PFCAs) and tetrabromobisphenol A. Average published R_PM values range from 0.14 to 1.02 (lipid-adjusted) and from 0.30 to 1.4 (based on wet weights). The broad R_CM and R_PM ranges may reflect effects of various factors, inter alia physicochemical properties of HOPs, metabolic capacities of mothers and fetuses, placental maturity, and differential expression of influx/efflux transporters in the placenta. Generally, HOPs’ R_CM values decline linearly with molecular size, and are curvilinearly related to solubility. Plasma protein binding affinity and the difference between maternal and fetal metabolic capacities may also affect some HOPs’ transfer efficiencies. HOPs’ molecular size may be influential. Transplacental transport of HOPs likely occurs mostly through passive diffusion, although influx/efflux transporters expressed on maternal and/or fetal sides of the placenta may also facilitate or hinder their transport. Overall, the review highlights clear gaps in our understanding of mechanisms involved in HOPs’ transplacental transport.

持久性卤代有机污染物（HOP）是一类有毒化学物质，可能通过从其母亲经胎盘转移而对胎儿产生不利影响。在这里，我们回顾了胎盘，母体和脐带血清中各种HOP（有机氯农药，多氯联苯，多溴联苯醚，短链和中链氯化石蜡以及全氟烷基和多氟烷基物质）的内部暴露水平。我们还对每种化合物的经胎盘转移和胎盘分布特征进行了分析，并讨论了几种因素对HOPs转移和积累效率的影响，以及HOPs跨胎盘屏障转移的主要机制。分别总结为_CM和R _PM）。HOP的平均已发布R _CM值范围为0.24至3.08（脂质调整后）和0.04至3.1（基于湿重），并且对于全氟烷基羧酸盐（PFCA）和四溴双酚A最高。平均已发布的R _PM值范围为0.14至1.02（脂质调节）和0.30至1.4（基于湿重）。宽的R _CM和R _PM范围可能反映了各种因素的影响，尤其是HOP的理化特性，母亲和胎儿的代谢能力，胎盘成熟度以及胎盘中内流/外向转运蛋白的差异表达。通常，HOP的R _CM值随分子大小线性下降，并与溶解度曲线相关。血浆蛋白结合亲和力以及母体和胎儿代谢能力之间的差异也可能影响某些HOP的转移效率。HOP的分子大小可能会产生影响。HOPs的胎盘转运可能主要通过被动扩散发生，尽管在胎盘的母胎和/或胎儿侧表达的涌入/外流转运蛋白也可能促进或阻碍其转运。总体而言，该评论突出了我们对HOP跨胎盘运输机制的认识上的明显差距。