Carbon filtering removes remaining contaminants and impurities by chemical absorption onto activated carbon. These fall into the categories of silt, inorganic contaminants, organic chemicals and pathogens. Exposure to pesticides and other environmental contaminants may be a significant contributing factor as well. These scales are very resistant to everyday shop contaminants and debris. It usually contains propylene glycol, glycerin, nicotine, flavorings, additives, and contaminants. See Part C for controls on toxic hazards from "ground contaminants" and/or "brownfield" development. Study continued into the varied effects of thermal comfort, oxygen, carbon dioxide, and biological contaminants. All these products have a very low content of sulfur and other contaminants. Next the water is run through a tank containing activated charcoal to adsorb organic contaminants. Some suspect fish consumption is a major source of many environmental contaminants. Willow trees and reeds absorb salt and other contaminants, effectively desalinating the water. This tank is meant to capture any remaining nuclear waste contaminants. EPA is considering developing a National Primary Drinking Water Regulation for these contaminants. Mattresses are also susceptible to many other contaminants. EPA also identifies and lists unregulated contaminants which may require regulation.