People of four generations ago lived at the turn of the 20th Century, before the invention and widespread use in agriculture and industry of thousands of synthetic chemicals. Those of us living in the early 21st Century inhabit a world where some of these substances – which were introduced as far back as the 1920s and employed more and more in the 1940s and '50s – have been around for decades. Now they are everywhere . . . including in the tissues of every human being on Earth.
