Many toxic pollutants can be characterised as “general” because they act on various parts of the environment (air, water, ground, biomass in food chains). Their potential hazard for organisms depends at each moment in time on their concentration and toxicity. A number of general pollutants that move by means of foods within the trophic chains appear in increasing concentrations from the lowest to the highest trophic levels. This phenomenon is known as biomagnification and can occur when pollutants are persistent, that is, when they do not break down or break down only with difficulty (e.g. metals, radioactive elements, stable organic compounds) and are not quickly eliminated by organisms. Biomagnification is due to a combination of the low rate at which the pollutants are eliminated or broken down and low energy efficiency all along the food chain (Chapter 4). The concentration of a persistent pollutant on one trophic level may appear on the next level increased by a factor even of the order of 10.