[Research advances in the transplacental transfer efficiencies of environmental pollutants]

Industrialization has led to significant increases in the types and quantities of pollutants, with environmental pollutants widely present in various media, including the air, food, and everyday items. These pollutants can enter the human body via multiple pathways, including ingestion through food and absorption through the skin; this intrusion can disrupt the production, release, and circulation of hormones in the body, resulting in a range of illnesses that affect the reproductive, endocrine, and nervous systems. Consequently, these pollutants pose substantial risks to human health. In particular, fetuses are highly sensitive to environmental pollutants during critical stages of development, and exposure during periods of growth and development can result in more-obvious and severe health hazards that can lead to preterm birth, low birth weight, and fetal malformations. The placenta acts as a barrier between the mother and fetus, and selectively filters certain pollutants. While some pollutants remain in the maternal bloodstream, others cross the placental barrier into the fetal umbilical blood through passive diffusion, placental transport proteins, or endocytosis. The transplacental transfer efficiency (TTE) is the ratio of the level of the pollutant in the umbilical blood to that in the maternal blood, and is a valuable metric for evaluating the ability of a pollutant to breach the placental barrier. A higher TTE implies that a larger proportion of pollutants are transferred from the mother to the fetus, thereby amplifying the potential risks to the fetus. Mass spectrometry-based detection methods are extensively used in the chemical and environmental sciences because they are exceptionally sensitive and highly resolving. This analytical technique involves ionizing compounds within a sample and identifying them based on their distinct mass-to-charge ratios; it enables both qualitative and quantitative analyses of various environmental pollutants. Current methodologies for examining the TTE of a pollutant include in-vitro experiments, animal studies, epidemiologic studies, and model calculation; these approaches help to evaluate the transfer of pollutants from mother to fetus via the placenta. Analyzing the TTEs of different chemicals enables high-risk pollutants to be identified and provides an understanding of their abilities to cross the placenta. Research on the transplacental transfer of environmental pollutants has focused mainly on per- and polyfluoroalkyl substances (PFASs), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs), with relatively few studies on the TTEs of other pollutants reported. Pollutant transfer through the placenta is a complex process that is influenced by factors that include the physical and chemical properties of the pollutant (e.g., molecular mass, solubility, and lipophilicity), maternal factors (e.g., maternal health and lifestyle, maternal genetics, environmental conditions, and socioeconomic status), and placental characteristics (e.g., placental maturity, placental blood flow, transport proteins, and metabolic enzymes). This review summarizes recent advances in research on the TTEs of environmental pollutants, focusing on analytical methods, the TTEs of PFASs, PBDEs, PCBs, and OCPs, and the pivotal factors that influence TTEs. Studying the TTEs of pollutants enables their characteristics to be elucidated, thereby providing support data for research on the exposure, transfer, and accumulation of pollutants in the human body, as well as a theoretical framework for understanding the mechanism of transplacental transfer of environmental pollutants. This research is expected to play a vital role in assessing the impact of environmental pollutants on the health of pregnant women and their fetuses.