Many chemists believe that GC-MS is the best tool for monitoring organic pollutants in the environment. The cost of GC-MS equipment has decreased a lot. The reliability of GC-MS has increased at the same time. Both improvements have increased use in environmental studies. Some compounds, such as certain pesticides and herbicides, cannot be identified by GS-MS. They are too similar to other related compounds. But for most organic analysis of environmental samples, including many major classes of pesticides, GC-MS is very sensitive and effective.