Malathion and chlorpyrifos are each likely to harm most of the 1,782 mammals, birds, fish, reptiles and plants listed under the Endangered Species Act

Almost all of the 1,700 most endangered plants and animals in the US are likely to be harmed by two widely used pesticides, an alarming new Environmental Protection Agency (EPA) analysis has found.

Malathion, an insecticide registered for use in the US since 1956, is likely to cause harm to 97% of the 1,782 mammals, birds, fish, reptiles and plants listed under the Endangered Species Act. Malathion is commonly used to treat fruit, vegetables and plants for pests, as well as on pets to remove ticks.

A separate pesticide, chlorpyrifos, is also a severe risk to 97% of America’s most threatened flora and fauna. Chlorpyrifos, which smells a little like rotten eggs, is regularly deployed to exterminate termites, mosquitoes and roundworms.

A third pesticide, diazinon, often used on cockroaches and ants, threatens 79% of endangered species. The EPA study is the first of its kind to look at whether common pesticides harm US wildlife.

The risk posed by malathion and chlorpyrifos is so widespread across the US that the few species considered not at risk are mainly those already classified as extinct, the EPA study found. In March last year, the World Health Organization said that malathion and diazinon are “probably carcinogenic to humans”.

Lori Ann Burd, environmental health director at the Center for Biological Diversity, said: “For the first time in history, we finally have data showing just how catastrophically bad these pesticides are for endangered species – from birds and frogs to fish and plants.

“These dangerous pesticides have been used without proper analysis for decades, and now’s the time to take this new information and create commonsense measures to protect plants, animals and people from these chemicals.”

Environmental groups and some farmers have been pushing the federal government to better explain the impact of pesticides upon wildlife and humans. There have been calls to ban seven organophosphate pesticides – used on corn, cotton, watermelon and wheat – due to evidence that they can cause cognitive problems in children and thousands of deaths among bird species.

In January, the EPA acknowledged that imidacloprid, one of the world’s most commonly used pesticides, can be harmful to honeybees, the most important pollinators of crops. Jonathan Lundgren, a senior entomologist, has accused federal agencies of suppressing negative research into the effects of pesticides. Federal officials have rejected the claims.

“The EPA has allowed chemical companies to register more than 16,000 pesticides without properly considering their impacts. That has to stop,” Burd said. “These evaluations are a huge step forward for the EPA. Now that we know the magnitude of danger these pesticides pose, it’s clear we need to take action.”

The EPA was contacted for comment on further action as a result of the studies.