<unk>  exposure may cause developmental defects, chronic illnesses, and death. Some are carcinogens per IARC, possibly including breast cancer. Many<unk> s are capable of endocrine disruption within the reproductive system, the central nervous system, or the immune system. People and animals are exposed to<unk> s mostly through their diet, occupationally, or while growing in the womb. For humans not exposed to<unk> s through accidental or occupational means, over 90% of exposure comes from animal product foods due to bioaccumulation in fat tissues and bioaccumulate through the food chain. In general,<unk>  serum levels increase with age and tend to be higher in females than males. Studies have investigated the correlation between low level exposure of<unk> s and various diseases. In order to assess disease risk due to<unk> s in a particular location, government agencies may produce a human health risk assessment which takes into account the<unk> s' bioavailability and their dose-response relationships. Endocrine disruption The majority of<unk> s are known to disrupt normal functioning of the endocrine system. Low level exposure to<unk> s during critical developmental periods of fetus, newborn and child can have a lasting effect throughout their lifespan. A 2002 study summarizes data on endocrine disruption and health complications from exposure to<unk> s during critical developmental stages in an<unk> m's lifespan. The study aimed to answer the question whether or not chronic, low level exposure to<unk> s can have a health impact on the endocrine system and development of<unk> ms from different species. The study found that exposure of<unk> s during a critical developmental time frame can produce a permanent changes in the<unk> ms path of development. Exposure of<unk> s during non-critical developmental time frames may not lead to detectable diseases and health complications later in their life. In wildlife, the critical development time frames are in utero, in ovo, and during reproductive periods. In humans, the critical development timeframe is during fetal development. Reproductive system The same study in 2002 with evidence of a link from<unk> s to endocrine disruption also linked low dose exposure of<unk> s to reproductive health effects. The study stated that<unk>  exposure can lead to negative health effects especially in the male reproductive system, such as decreased sperm quality and quantity, altered sex ratio and early puberty onset. For females exposed to<unk> s, altered reproductive tissues and pregnancy outcomes as well as endometriosis have been reported. Gestational weight gain and newborn head circumference A Greek study from 2014 investigated the link between maternal weight gain during pregnancy, their PCB-exposure level and PCB level in their newborn infants, their birth weight, gestational age, and head circumference. The lower the birth weight and head circumference of the infants was, the higher<unk>  levels during prenatal development had been, but only if mothers had either excessive or inadequate weight gain during pregnancy. No correlation between<unk>  exposure and gestational age was found. A 2013 case-control study conducted 2009 in Indian mothers and their offspring showed prenatal exposure of two types of<unk> hlorine pesticides (HCH, DDT and DDE) impaired the growth of the fetus, reduced the birth weight, length, head circumference and chest circumference. Additive and synergistic effects Evaluation of the effects of<unk> s on health is very challenging in the laboratory setting. For example, for<unk> ms exposed to a mixture of<unk> s, the effects are assumed to be additive. Mixtures of<unk> s can in principle produce synergistic effects. With synergistic effects, the toxicity of each compound is enhanced (or depressed) by the presence of other compounds in the mixture. When put together, the effects can far exceed the approximated additive effects of the<unk>  compound mixture.
Persistent organic pollutant
Corrosive substance
Organochlorine compound
Drug 
Drug
Toxic heavy metal
Biological agent
Toxicant