Some toxicant are particulararly dangerous- Resist Degradation- travel quickly Radioactive Isotopes, some pesticides, PB Dec. 5, PCBS, DDT (dichlorodiphenyltrichloroethane) -Pesticide banned in the US in 1972. Causes banned in the US in 1972, causes banned in the US in 1972, causes birds to lay eggs with thin shells. Impact of DDT: Persistence- substance is very stable, takes years to break down. Bio accumulation: build of a toxicant overtime. Cannot be metabolized, cannot breakdown in the environment. Problem wen dealing with food chains. Top carnivores most at risk: Biological magnification- increase of toxicant – shrimp – eel- needlefish- gull- impact, significantly effect reproduction system. Amount of DDT in tissue vs. trophic level. * movement and fate of toxicant *Persistant Organic Pollutants* dose and response: Lethal dose, Sub Lethal dose, Effective Dose, Threshold Dose. How to determine the health effects on pollutants- threshold! woah! yea! wow! Risk assessment Chemicals: Single tests vs. multiple exposure, interactions: Addivity combined effects of two substances add up. Synergy: combined effect of substance is greater than expected- Antagonism: Combined effect of substances is smaller than expected.