2. heavy metals that pose health hazards to people and ecosystems occur a. as a by-product of agriculture b. over extended periods of time c. very quickly with tragic results d. all of the above

The appropriate answer is doing. All of the above. Heavy metals are sometimes used in agricultural chemicals and can contaminate both terrestrial and aquatic ecosystems. Heavy metal concentrations can build up overtime as industrialization progressed. Chemical spills can introduce heavy metals to ecosystems quickly with devastating effects.