Defining 'persistent organic' dangers

"There was a strange stillness. The birds, for example - where had they gone? It was a spring without voices."

The scenario that US biologist and conservationist Rachel Carson depicted in her 1962 book Silent Spring could become a reality if governments slacken efforts to eliminate the production and use of persistent organic pollutants, environmental experts warn.

There are a few natural sources of POPs but the substances are mostly the result of industrial processes.