<unk>  is any structural or functional alteration, reversible or irreversible, which interferes with homeostasis, normal growth, differentiation, development or behavior, and is caused by environmental insult (including drugs, lifestyle factors such as alcohol, diet, and environmental toxic chemicals or physical factors). It is the study of adverse effects on the development of the organism resulting from exposure to toxic agents before conception (either parent), during prenatal development, or post-natally until puberty. The substance that causes<unk>  from embryonic stage to birth is called teratogens. The effect of the<unk>  toxicants depends on the type of substance, dose and duration and time of exposure. embryogenesis in humans. Beginning at the fertilized egg, ending with the closing of the neural tube. The embryogenesis is the most crucial time for the action of any teratogenic substances resulting in birth defects. 228x228px Certain pathogens are also included since the toxins they secrete are known to cause adverse effects on the development of the organism when the mother or fetus is infected.<unk>  toxicology is a science studying adverse<unk>  outcomes. This term has widely replaced the early term for the study of primarily structural congenital abnormalities, teratology, to enable inclusion of a more diverse spectrum of congenital disorders. Typical factors causing<unk>  are radiation, infections (e.g. rubella), maternal metabolic imbalances (e.g. alcoholism, diabetes, folic acid deficiency), drugs (e.g. anticancer drugs, tetracyclines, many hormones, thalidomide), and environmental chemicals (e.g. mercury, lead, dioxins, PBDEs, HBCD, tobacco smoke). The first-trimester exposure is considered the most potential for<unk> . Once fertilization has taken place, the toxicants in the environment can pass through the mother to the developing embryo or fetus across the placental barrier. The fetus is at greatest risk during the first 14th to 60th day of the pregnancy when the major organs are being formed. However, depending on the type of toxicant and amount of exposure, a fetus can be exposed to toxicants at any time during pregnancy. For example, exposure to a particular toxicant at one time in the pregnancy may result in organ damage and at another time in the pregnancy could cause death of the fetus and miscarriage. There are a number of chemicals, biological agents (such as bacteria and viruses), and physical agents (such as radiation) used in a variety of workplaces that are known to cause<unk>  disorders.<unk>  disorders can include a wide range of physical abnormalities, such as bone or organ deformities, or behavioral and learning problems, such as a mental retardation. Exposures to some chemicals during pregnancy can lead to the development of cancer later in the life of the child and are called transgenerational carcinogens. Exposure to toxicants during the second and third trimesters of a pregnancy can lead to slow fetal grown and result in low birth weight.
Developmental toxicity
Neurotoxicity
Chromosome instability
Environmental disease
Undervirilization
Mitochondrial toxicity
Acute toxicity
Genotoxicity