Polychlorinated biphenyls (PCBs) were widely used as dielectric and coolant fluids, for example in transformers, capacitors, and electric motors. Due to PCBs' environmental toxicity and classification as a persistent organic pollutant, PCB production was banned by the United States Congress in 1979 and by the Stockholm Convention on Persistent Organic Pollutants in 2001. According to the U.S. Environmental Protection Agency (EPA), PCBs have been shown to cause cancer in animals, and there is also evidence that they can cause cancer in humans. A number of peer-reviewed health studies have shown an association between exposure to PCBs and non-Hodgkin Lymphoma, a frequently fatal form of cancer. However, other similar studies have found no such link. Studies of PCB workers have uniformally shown no statistically significant increased rates of deaths from non-Hodgkin Lymphoma. In 2013, The International Association for Research on Cancer (IARC) determined that the evidence that PCBs cause non-Hodgkin Lymphoma is “limited” and “not consistent.” Institutions devoted to cancer research and treatment such as the American Cancer Society and the Mayo Clinic do not list PCB exposure as a risk factor for non-Hodgkin Lymphoma.
Concerns about the toxicity of PCBs are largely based on compounds within this group that share a structural similarity and toxic mode of action with dioxin. Toxic effects such as endocrine disruption and neurotoxicity are also associated with other compounds within the group. The maximum allowable contaminant level in drinking water in the United States is set at zero, but due to water treatment technologies a level of 0.5 parts per billion is the defacto level.
Building material is any material which is used for construction purposes. Many naturally occurring substances, such as clay, rocks, sand, and wood, even twigs and leaves, have been used to construct buildings. Apart from naturally occurring materials, many man-made products are in use, some more and some less synthetic. The manufacture of building materials is an established industry in many countries and the use of these materials is typically segmented into specific specialty trades, such as carpentry, insulation, plumbing, and roofing work. They provide the make-up of habitats and structures including homes.]citation needed[
Brush structures are built entirely from plant parts and are generally found in tropical and sub-tropical areas, such as rainforests, where very large leaves can be used in the building. These are built mostly with branches, twigs and leaves, and bark, similar to a beaver's lodge. These were variously named wikiups, lean-tos, and so forth.]citation needed[