Portfolio 21 does not invest in companies exclusively involved in mining or in diversified companies that derive more than a small percentage of revenues from mining or other extractive operations. By nature, the metals and mining industry has enormous ecological impacts. Mining requires access to large volumes of water and generates large volumes of waste. Proper management of waste is often difficult, creating numerous liabilities in the form of spills and releases, surface water runoff, and contamination. Mining is also labor intensive and takes place in challenging environments, often in countries with varying safety standards and in areas that infringe on culturally significant land. Mining companies are also increasingly operating in politically unstable regions where risks of corruption are high. Portfolio 21 will make exceptions to this policy for the steel sub-industry, which is categorized within the metals and mining industry. Portfolio 21 may invest in companies that exclusively use recycled steel as their raw material input.