How does the toxicity of DDT change as it moves up the food chain?

The reason for this is bioaccumulation and biomagnification. But why would DDT increase up the food chain? Lets consider this, You have ten phytoplanktons that contain high levels of DDT. The problem arises with the fact that your secondary food chain, your primary consumer MUST consume all of these 10 phytoplanktons to not starve. So now 1 fish has eaten 10 phytoplanktons, so it currently contains 10x the amount of DDT as compared to each phytoplankton alone. Now say a bigger fish eats ten of these fishes to survive then it has now eaten 100 phytoplanktons and so on. I hope you get the logic.