by killing shark food with toxins

The top of the food chain.

As organisms consume other organisms, the toxins are all passed up in the food chain. Therefore, the top of the food chain will have the highest concentration of toxins.

it reproduses on the food and spreads its toxins

The best way to prevent ingesting harmful toxins is to wear a face mask of some sort when working around the toxins. If you have a fear of ingesting toxins from common food sources you can always read the ingredient label that comes with most food.

Undigested food, toxins bacteria