Everywhere they look, they find particles of pollution, like infinite spores in an endless contagion field. Scientists call that field the "exposome": the sum of all external exposures encountered by each of us over a lifetime, which portion and shape our fate alongside genes and behavior. Plastic is now threaded through the flesh of fish, where it is interfering with reproduction, and the stalks of plants, where it is interfering with photosynthesis, and in much else we place upon our dinner plates and set about eating. There might be plastic in your saliva, and almost certainly in your blood. Plastic has been found in human hearts and kidneys and other organs, in the breast milk expressed by new mothers and on both sides of their placentas. The penetration appears so complete that some researchers have begun to worry that their methods, too, are compromised by ambient contamination and plastic materials in the lab. The buildup inside brain tissue has grown 50 percent in just eight years, and that, as of last year, there might be inside your skull the equivalent of a full plastic spoon " by weight perhaps one-fifth as much polymer as there is brainstem in there. Beyond plastics, there is PFAS, that category of long-lasting industrial compounds often called "forever chemicals." Whole environmental movements of the past have been built on fears of incipient contamination. But what are the lessons when pollution is seemingly everywhere, and in everyone, already?