Final answer:
The most harmful diesel engine coolant to humans among the given options is Ethylene Glycol (EG) due to its toxicity and potential to convert into oxalic acid upon ingestion, which can cause serious health issues, including kidney stones and even fatality.
Step-by-step explanation:
When discussing types of diesel engine coolants and their potential harm to human health, we need to consider the toxicity of the various compounds used to prevent freezing and overheating in engines. Specifically, we are comparing polyethylene glycol (PG), waterless engine coolant (WEC), ethylene glycol (EG), and extended life coolant (ELC).
Ethylene glycol (EG) is a common ingredient used in antifreeze and coolant solutions. Despite its effectiveness in lowering the freezing point and raising the boiling point of the engine's coolant, ethylene glycol is hazardous. Upon ingestion, it metabolizes into oxalic acid in the body, which can lead to the formation of kidney stones and other severe health issues, including potential fatality if not treated promptly. It is important to note that ethylene glycol has a sweet taste, which makes it particularly dangerous as it can lead to accidental or intentional ingestion.
Other coolant types, such as propylene glycol-based coolants, have become more prevalent due to their significantly lower toxicity compared to ethylene glycol. Over the years, various other coolants have been developed to provide similar or better performance with less risk to human health and the environment.
Considering the information provided and the well-documented toxicity of ethylene glycol, it is regarded as the potentially most harmful to humans among the options given. Therefore, the correct option is c) Ethylene Glycol - EG, which should be handled carefully to avoid accidental poisoning.