An article in The Sun weighing the hazards of regularly eating fish mentioned prominently the risks of consuming "trace amounts of mercury, PCBs, dioxin and other toxins," referring later to "toxins such as mercury." On balance, fish in the diet is a good thing for most people, but a potential hazard for certain groups.

The problem here is that while toxic and toxin may be roughly interchangeable in ordinary discourse, the words have more precise meanings in scientific contexts. A toxin is a poisonous substance produced by a living organism. The strain of E. coli (Escherichia coli) in our intestines that happily and harmlessly produces vitamins for us is fine. But if a harmful strain, say, from cattle, should contaminate the spinach crop and, once ingested, produce toxins, we have trouble.

Mercury, an element, is not an organic product, but it is highly toxic, or poisonous. So is lead. So are many industrial products and byproducts that get loose in the environment. But they are not toxins.

Toxins are toxic — that is, poisonous—but not all toxic substances are toxins.

The point this lapse illustrates is the difficulty of writing on technical subjects for a general-audience publication. In writing about science and medicine — business or sports or law — we struggle to make technical subjects readily comprehensible to the non-specialist reader, while trying not to bring the scorn of the specialist down on our heads.