It is unclear how much collecting amphibian populations can sustain or what would be a sustainable harvest. In many jurisdictions in Canada even the number of frogs collected each year isn't known. In addition to the direct effects, acid rain also mobilizes other toxins into ponds, poisoning eggs, larvae and juveniles. Some amphibians thrive in agricultural areas enjoying the benefits of irrigation and artificial ponds for watering livestock. Nonetheless the increasing use of pesticides poses a threat.
Pesticides can also have lethal effects years after their use.
For example, it has been over 20 years since DDT was banned in Canada and yet it is commonly found in the tissues of many amphibians in certain areas. Ironically, irrigation and artificial ponds may actually attract amphibians to breed in sites where their chance of success is low. Chemicals A number of chemical contaminants are hard to detect and study because they rarely outright kill their victims. In some fish and reptiles these contaminants interfere with reproduction and can even cause sterility. Toxicologists continue to try and understand this complex subject, but meanwhile we continue to emit more and new kinds of these contaminants into our environment.