Safer than we think.
The article on organohalogens in 1920s whale oil ("A Whale's Tale: Puzzling marine compounds are natural," SN: 10/28/06, p. 278) indicates both the stability of such natural products and their bioaccumulation in organisms at the top of the food chain. It is no doubt prudent that human activity--i.e., chemical manufacturing--should not increase the quantity of these chemicals in the oceans. But it should be recalled that banning of PCBs and similar substances was based solely on the fears aroused by their stability. Their human toxicity is relatively low. Continued information of the kind reported is valuable in that it indicates we live in a chemical world. ANTHONY TREWAVAS, EDINBURGH, SCOTLAND