Diffused air systems are prone to problems of particulate buildup, rust-producing bacteria, and other contaminants, which can clog a system and shut it down. The air must be put under considerable pressure to get it into the bottom of the diffusion basin, hence diffusion systems are limited to relatively low air-to-water ratios. As a result diffused aeration systems can only cost-effectively remove highly volatile contaminants, like radon, and are more often used for the purpose of introducing oxygen or ozone into the water.