How do phosphates kill plants?
Phosphate itself shouldn’t kill a plant – the phosphorous, and phosphate are used as part of the DNA and RNA molecules, and it’s a part of ATP, the energy transfer molecule. If anything, phosphorous in the form of phosphate is a plant fertilizer. The only case where phosphate/phosphorous should be detrimental to plants is in an aquatic environment where it fertilizes algae growth. As the algae overgrows plants beneath it (and other parts of the algal mass) these are shaded from sunlight, and prevented from using photosynthesis to make food. These will die, and their decomposition uses up dissolved oxygen from the water, making the environement unsuitable for fish.
