There is little research about the combined effects of commonly used chemicals. Young children (including the unborn) are particularly vulnerable to chemical exposure due to their body size, rapidly developing brains, hormonal and nervous systems, and behaviors (such as crawling on the ground and putting Searchable PDF created by OCR.space (Free Version) their fingers in their mouths). Cats and dogs that play in or eat chemically treated grass absorb chemicals through their skin or digest them. Some pets have been fatally poisoned or developed higher rates of cancer. Cats are very sensitive to such chemicals and when exposed to pesticides become noticeably more aggressive (Rachel Carson Council).
Chemicals used in lawn and yard care do not stay where they are applied. When applied to the ground, chemicals can be carried into buildings and cars on shoes and paws. Without exposure to sunlight and water, they breakdown very slowly and can remain for months in carpets, toys, and dust bunnies.
Chemicals also move in the environment. Rainwater washes them down streets and storm drains to streams, wetlands, lakes, and oceans. Rainwater soaking into the ground carries fertilizers and pesticides into groundwater, contaminating wells and aquifers. Pesticides absorbed by plants or insects can accumulate in the food chain as birds. Fish, other wildlife, or people feed on the contaminated organisms. When chemicals are sprayed, breezes can carry the droplets to neighboring properties or even miles away. Cleaning sprayers and dumping the wash water down the drain sends pesticides and fertilizers directly into a septic system (and the groundwater) or a sewage treatment plant (and the local river).