Water quality tests from a local river show low levels of a single heavy metal. The level of heavy metal in the water is under the acceptable legal limit and does not affect the local population's drinking water. The residents of the next town, down river from the first town, are suffering from numerous stomach ailments and are showing signs of long-term kidney damage. Water quality tests in the river by the second town show two types of heavy metals in the water. One of the metals is the same as the metal in the first town. What can scientists infer about the possible reason for the illnesses in the second town? More metals cause acute effects but not chronic effects. The first metal causes an acute effect compared to the other. The heavy metals have a synergistic relationship when combined. The heavy metals have an antagonistic relationship when combined.