The Aluminum Association has followed closely the developing knowledge of health effects of aluminum and aluminum compounds, particularly the recent neurological implications. The Kettering report concluded that there was no direct clinical or experimental evidence that aluminum is neurotoxic to humans or animals under ordinary conditions of environmental exposure. The Food and Drug Administration (FDA) publishes a Total Diet Study which lists 235 foods commonly eaten in the US. Aluminum compounds are present in air coming from various sources, such as dry soil, coal combustion and cigarette smoke. The gastrointestinal tract is only very slightly permeable to aluminum and provides a relatively effective barrier to its absorption. Investigators continue to study the effects of direct injections of aluminum powder and aluminum salts into animal brains in order to bypass the body's controls. A conference on Aluminum Analysis in Biological Materials, co- sponsored by the Aluminum Association and the University of Virginia, was held in June 1983.