Heavy metals in maternal and cord blood in Beijing and their efficiency of placental transfer

Abstract

This study aimed to determine the effect of exposure to heavy metals in pregnant women in Beijing, China. We also evaluated the association of these heavy metals with birth weight and length of newborns. We measured the levels of 10 heavy metals, including lead (Pb), titanium (Ti), manganese (Mn), nickel (Ni), cadmium (Cd), chromium (Cr), antimony (Sb), stannum (Sn), vanadium (V), and arsenic (As), in 156 maternal and cord blood pairs. An inductively coupled plasma mass spectrometry method was used for measurement. Pb, As, Ti, Mn, and Sb showed high detection rates (> 50%) in both maternal and cord blood. Fourteen (9%) mothers had blood Pb levels greater than the United States Center for Disease Control allowable threshold limit for children (50 μg/L). In prenatal exposure to these heavy metals, there was no significant association between any heavy metal and birth weight/length. Moreover, we estimated the placental transfer efficiency of each heavy metal, and the median placental transfer efficiency ranged from 49.6% (Ni) to 194% (Mn) (except for Cd and Sn). The level and detection rate of Cd in maternal blood were much higher than that in cord blood, which suggested that Cd had difficulty in passing the placental barrier. Prospective research should focus on the source and risk of heavy metals in non-occupationally exposed pregnant women in Beijing.

Introduction

Heavy metals are ubiquitous environmental pollutants, which results from industrial pollution, human activities, and natural combustion (Al-Saleh et al., 2011, Amaya et al., 2013). Dietary intake is the most common source of heavy metals for the general population (Amaya et al., 2013). Itai-Itai disease, which occurs in Japan, first brought global public attention to the problem of cadmium (Cd)-contaminated rice (Nogawa and Kido, 1993). In the US, several million people are suffering in arsenic (As) exposure of drinking water (Ayotte et al., 2011). The As concentration in these drinking water is above the US Environmental Protection Agency standard for As in drinking water systems (10 μg/L). Recently, low As exposure levels were reported to be associated with the risk of hyperuricemia in men and with the prevalence of gout in women (Kuo et al., 2015). However, for some heavy metals, such as vanadium (V) and stibium (Sb), their safe and adequate limit of intake is not known for humans (Imtiaz et al., 2015). To date, the adverse effect of heavy metals on human is gradually acknowledged because of their known and potential toxic properties.

Epidemiological evidence has demonstrated that some heavy metals exposure can dramatically affect adult fertility (Al-Saleh et al., 2008, Amaya et al., 2013, Kuo et al., 2015, Jin et al., 2016). Maternal blood lead (Pb) levels of approximately 100 μg/L would increase the risks of pregnancy hypertension and spontaneous abortion in pregnant women, and reduce neurobehavioral development in offspring (Bellinger, 2005). A recent study reported that Cd concentration in maternal blood was inversely associated with the birth weight of offspring in Bangladesh (Menai et al., 2012). Jin et al., (2014) conducted that high Cd level in pregnant women’ blood would increase the risk of neural tube defects in newborns.

The placenta is an important selective barrier to toxic compounds during pregnancy (Al-Saleh et al., 2011), however, some heavy metals can interfere with placental transport systems (Zhang et al., 2004) and then cross through the placenta (Osman et al., 2000). Because of differences between the fetus and adult in many biochemical pathways, the fetus is highly sensitive to chemicals or drugs, even at a very low exposure concentration (Wells et al., 2010). Therefore, there is a growing concern about the adverse effect on the fertility or fetal development even that the exposure level of heavy metals was much lower than international guidelines (Greet et al., 2006, Holmes et al., 2009, Al-Saleh et al., 2011). Furthermore, Mattison (2010) suggested that there were no thresholds for the effects of environmental exposure in utero or during early childhood.

To evaluate of the exposure of heavy metals exposure during pregnancy, maternal and/or cord samples was mainly used (Butler Walker et al., 2006, Amaya et al., 2013, Jin et al., 2014, Jin et al., 2016). Cord blood mercury levels are usually higher than that of maternal blood (Gundacker et al., 2010). Cord blood Pb levels are equal to or lower than maternal blood Pb levels (Ask et al., 2002, Al-Saleh et al., 2011), while cord blood Cd levels are always much lower than maternal blood Cd levels (Kantola et al., 2000, Al-Saleh et al., 2011). Currently, little is known about the features and mechanisms involved in heavy metal toxicokinetics through the placenta.

In this study, we conducted a pilot study of 156 pairs of maternal and cord blood samples that collected in Beijing, China. We aimed to characterize the occurrence, distribution, and placental transport of 10 heavy metals, including Pb, Cd, As, titanium (Ti), V, chrome (Cr), manganese (Mn), nickel (Ni), stannum (Sn), and Sb. Moreover, the association between each heavy metal and birth weight/length of newborns was investigated.