We know pesticides are harmful to the environment, but how harmful are pesticides to human health? Some highly toxic pesticides, such as DDT, have been banned. But according to the Pesticide Action Network North America (PANNA), there many still in use today are associated with serious health issues such as neurological damage, birth defects, developmental or behavioral issues (such as autism and ADHD), and even certain types of cancer. One recent study showed that birth defects such as spina bifida, cleft lip, clubfoot, and Down's syndrome are most common in children conceived during the spring and summer, when agricultural pesticide use is at its peak. And pesticides may contribute to male infertility, according to a new study published in Environmental Health Perspectives. Here is a look at two of the worst offenders.

Pesticide: Atrazine

Used on:Corn, sugarcane, and grain crops.

What it is:Banned in France, Germany, Denmark, Norway, and Sweden, atrazine is the second most widely used pesticide in the U.S. Exposure can cause cardiovascular damage, muscle spasms, adrenal gland damage, and eye or skin irritation. It is a possible endocrine disrupter and carcinogen.

Pesticide: Dursban

Used on:Corn, cotton, almonds, alfalfa, oranges, and walnuts.

What it is:Dursban is the brand name for chlorpyrifos, which belongs to a group of chemicals known as organophosphates. It is a suspected endocrine disruptor and can have neurological effects including excessive salivation, nausea, diarrhea, headaches, confusion, and dizziness. At high doses, chlorpyrifos cause convulsions, respiratory paralysis, coma, and even death. The EPA has banned most non-agricultural uses of dursban (such as in flea collars and to combat termites).