These common but toxic chemicals are long-lasting in the environment and harmful to every living organism they encounter. The term pesticide generally includes herbicides, insecticides, and fungicides. The purpose of these chemicals is to eradicate living organisms that may be considered undesirable. Pesticides can enter water systems from residential lawns, golf courses, public green-space, or agricultural land. They are often carried to the water with precipitation (rain or snow melts).
When pesticides reach the water, they can cause varying degrees of harm to organisms - the extent of the impact depends on the type of pesticide that is present. The adverse impacts of these chemicals are diverse, and can include tumors, skin conditions, weakened immune systems, reproductive problems, and even death. Pesticides are having an impact on a global scale; amphibian declines all over the world are being at least partially attributed to pesticide use. Pesticides containing a chemical called atrazine have been shown to change developing tadpoles into hermaphrodites, and to demasculinize tadpoles. Most pesticides have a tendency to accumulate over time within organisms and then in the organisms that eat them (this is called: bioaccumulation). This process can cause increasingly severe problems for organisms higher up in the food chain.
Fortunately, the Government of Ontario banned the sale and use of commercial pesticides in 2007. As a result, most homeowners and commercial lawn care experts are unable to use pesticides. Agricultural use of pesticides is not prohibited however, and remains an issue with regards to stream health.
There are many natural alternatives to using pesticides. Using specific plants, in the correct numbers and in the right places will significantly reduce the need to use pesticides. There are also methods of catching weeds before they spread, thus eliminating the need for spraying herbicides. In food gardens, a technique known as companion planting can help reduce insects and disease without the need for chemicals.