A team of researchers has found potentially dangerous levels of mercury and arsenic in Lake Baiyangdian, the largest lake in the North China Plain and a source of both food and drinking water for the people who live around it.

Contaminated fish are showing up lower on the food chain, a worrying sign that pollution is growing worse, not better in the world's largest freshwater reservoir.

Food chains, also called food webs, food networks and/or trophic networks, describe the feeding relationships between species to another within an ecosystem. Organisms are connected to the organisms they consume by arrows representing the direction of biomass transfer. Typically a food chain or food web refers to a graph where only connections are recorded, and a food network or ecosystem network refers to a network where the connections are given weights representing the quantity of nutrients or energy being transferred.