Which characteristic is primarily used to evaluate the toxicity of waste?

The concentration of harmful substances is the primary characteristic used to evaluate the toxicity of waste because it directly indicates the level of harmful chemicals or pollutants present in the wastewater. This measure provides insight into the potential impact on human health, aquatic life, and the environment. Higher concentrations of toxic substances can have more severe effects, making it crucial for treatment processes to effectively target and reduce these harmful components.

In contrast, while the volume of waste produced, the presence of organic matter, and the quality of incoming water are all important factors in assessing overall wastewater characteristics and treatment needs, they do not specifically quantify toxicity in the same manner. The concentration of harmful substances offers a more precise evaluation of how toxic the waste is, guiding operators in making decisions about treatment methods and regulatory compliance.