Human placenta as a 'dual' biomarker for monitoring fetal and maternal environment with special reference to potentially toxic trace elements. Part 1: physiology, function and sampling of placenta for elemental characterisation.

Choice of specimen from human subjects for monitoring pollutants proven to be detrimental to human health depends on the criteria chosen, namely real-time monitoring (RTM) or long-term monitoring (LTM). Specimens such as whole blood, urine, saliva and breast milk are commonly used from living subjects for RTM of toxic metals. However, sampling blood requires an invasive procedure. On the other hand, hair (with some limitations), bone (especially for the assessment of bone seeking elements), adipose tissue (mainly for organic pollutants) and liver (for both organic and inorganic toxicants) are used as specimens for LTM. With the exception of hair, generally these specimens are obtained at post-mortem. In context of health-related biomonitoring, placenta as a specimen has not received as much attention as it deserves. It is a unique sample requiring no invasive procedure, and offers possibilities for RTM, in particular as a dual purpose specimen for evaluating the pollutant burden exerted on the mother as well as on the fetus. Obtaining representative samples of placenta for elemental composition studies is a difficult task, because of heterogeneous mix of placental cells and decidual matter tainted with maternal and fetal blood. Therefore, the present sampling practices for placental tissue, and guidelines to safeguard the validity of the sampled material have been reviewed in part 1 with the following conclusions: medico-legal and ethical matters should be properly addressed before collecting the placenta; it is advisable to collect the entire placenta even if it includes the umbilical cord; further preparatory work is to be carried out in a clean laboratory and depends upon the purpose of the investigation; homogenising the entire sample may prove to be technically challenging but this step is crucial to obtain representative samples, handling the entire sample may be unavoidable; and an alternative method of procuring representative samples would require random samples from multiple sites, pooled, homogenised and assayed to confirm homogeneity.