Analyzing Incorrect Toxicity Statement
This question requires identifying the incorrect statement among the given options regarding the toxicity and classification of specific substances. Let's analyze each statement:
- Chromium (VI) toxicity: Statement 1 is correct. Chromium (VI) compounds are well-known for their high toxicity and carcinogenic properties.
- Methyl mercury toxicity: Statement 2 is correct. Methyl mercury is recognized as the most toxic species of mercury, readily crossing biological membranes and accumulating in the food chain.
- Arsenic (III) vs. Arsenic (V) toxicity: Statement 3 is correct. Arsenic in the +3 oxidation state (e.g., arsenite) is generally more toxic than Arsenic in the +5 oxidation state (e.g., arsenate) because it interferes more readily with cellular processes.
- Cadmium classification: Statement 4 claims that Cadmium is a criteria pollutant. This statement is incorrect. While Cadmium is a highly toxic heavy metal and regulated under environmental laws (like the Clean Air Act as a Hazardous Air Pollutant - HAP), it is not one of the six specific "criteria pollutants" for which the EPA sets National Ambient Air Quality Standards (NAAQS). The criteria pollutants are ozone, particulate matter, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead.
Therefore, the incorrect statement is that Cadmium is a criteria pollutant.