Few animals spark more emotional response from people than do dolphins.
And few events in the animal world strike people as more tragic than the occasional mass deaths of the sleek marine mammals. Dolphin die-offs are frequently attributed to viruses, bacteria or parasites, suggesting outbreaks that are natural in origin. In recent years, however, scientists have assembled evidence that the real culprit in many dolphin deaths might be pollution in coastal waters. Each is in a class of chemicals known as organic chlorine compounds. The two substances are long-lived in the environment and are known to suppress dolphins' immune systems, making them more vulnerable to disease.