Background: In recent years, the major concern has been focused on persistent organic pollutants (POPs), which are present in ecosphere in increasing concentrations, especially since 1950s. Among of these pollutants are dioxins and polychlorinated biphenyls (PCBs) released during vast burning and plastics processing, as well as pesticides which were industrial chemicals intensively produced for many years.
Results: In last decade, dioxins together with PCBs and pesticides have been classified as endocrine disrupting chemicals, because they are able to alter hormone-dependent processes and disrupt functioning of endocrine glands, e.g. thyroid and gonads. Furthermore, these pollutants have been included in neural disrupting chemicals due to their ability of altering neural transmission and formation of neural networks. Since POPs may persist in the environment for dozens of years, an exposure to these organic pollutants creates a serious issue for environmental toxicologists. POP intoxication creates severe clinical problems, which became evident in dramatic circumstances, e.g. Yusho incident in Japan, Yu-Cheng incident in Tajwan, Michigan Lake poisoning. Clinical problems have been recognized as disruption of thyroid and gonadal functions, immunodeficiency as well as psychomotor deficits and increased occurrence of hormone-dependent cancers. Thus, knowledge on POP effects on human nervous system has been related mainly to toxic effects of these organic pollutants. Little is known, however, about the action of very low, so called background, doses of POPs and their effects on hormonal homeostasis in developing brain. It is of particular importance, because doses which are low for adults might become toxic for fetuses, infants or children. Recently, the public concern has been focused on POP effects on brain function, concomitantly with the increase in neuropsychiatric disorders, including autism, attention deficit and hyperactivity disorder (ADHD) as well as learning disabilities. Although some of epidemiological data are controversial, most of them point to adverse effects of prenatal exposure to polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAH) on cognitive function and, in general, mental development of infants and children. Studies on prenatal exposure to pesticides demonstrated increased incidence of autism and ADHD as well as deficits in psychomotor and visio-spatial skills, which were observed in infants and 8 years old children, respectively. Psychomotor deficits were also indicated in 6 months old infants exposed prenatally to polychlorinated dibenzo-p-dioxin (PCDD) and in 1-6 year old children affected prenatally by polybrominated difenyl ethers (PBDE). Recent data also demonstrate the strong correlation between exposure to bisphenol A at early pregnancy and increased locomotor activity and aggressiveness of children.
Conclusions: Our knowledge on POP effects on human nervous system seems rather extensive, but is related mainly to toxic effects of these organic pollutants. Little is known, however, about the action of very low doses of POPs and their effects on hormonal homeostasis in developing brain. Therefore, the role of scientists and clinicians is to recognize the mechanisms of POP action, especially in respect to prenatal and early postnatal period when the nervous system develops and is particularly sensitive to hormonally active chemicals present in the environment.