Which characteristic is important for a substance to be considered hazardous waste?

For a substance to be designated as hazardous waste, it is crucial that it be a material no longer serving its intended purpose. This characteristic indicates that the substance is waste, as it is no longer needed or usable in its original function. Hazardous waste typically encompasses materials that, when discarded, may pose a threat to human health or the environment because of their chemical properties, such as being toxic, corrosive, reactive, or ignitable.

While the other characteristics may apply to certain types of waste or highlight other important considerations, they do not directly define hazardous waste. For example, a substance being recyclable is a positive trait that promotes sustainability but does not determine if it is hazardous. Similarly, a substance being a known toxin is relevant; however, there are many hazardous wastes that are not classified solely based on known toxicity. Additionally, ease of disposal is not a defining characteristic; hazardous wastes often require specialized handling and disposal methods due to their potential risks. Consequently, the key aspect is that the substance is no longer needed, resulting in its classification as waste, which can then lead to further assessment of its hazardous characteristics.