Using wastewater for irrigation of consumable plants may present a health hazard if it contains:

Using wastewater for irrigation of consumable plants can pose health hazards primarily due to the presence of certain contaminants, notably heavy metals like cadmium. Cadmium is a toxic element that can accumulate in the soil and subsequently be taken up by plants, entering the food chain. High levels of cadmium exposure can lead to serious health issues in humans, including kidney damage, bone fragility, and increased risk of cancer.

While nitrates, iron, and chlorides can have their own effects on plant health and water quality, they do not present the same degree of direct health hazard when consumed by humans as cadmium does. Nitrates, for example, can lead to methemoglobinemia (blue baby syndrome) in infants but are generally less immediately harmful than cadmium when present in wastewater. Iron is an essential nutrient that, although potentially harmful in excessive amounts, does not pose the same level of risk as cadmium. Chlorides can affect plant growth and water salinity but are not directly toxic to humans at common exposure levels.

Therefore, the health risks associated with using wastewater that contains cadmium underscore its importance as a contaminant of concern in agricultural practices involving consumable plants.