Final answer:
Lead and arsenic are examples of contaminants that can be harmful at extremely low concentrations such as parts per billion. Regulatory agencies set Maximum Contaminant Levels to protect public health, as even trace amounts of some chemicals can pose significant risks.
Step-by-step explanation:
Understanding the harm different contaminants can cause at low concentrations is crucial for safeguarding human health. Among various pollutants, certain substances are known to be toxic at minute levels. Take, for instance, lead. It has been scientifically established that lead levels as small as 15 parts per billion (ppb) can lead to significant health issues. This is a stark representation that even in trace amounts, some contaminants are incredibly harmful.
Arsenic is another contaminant that can be extremely harmful at very low exposure levels. The World Health Organization (WHO) has recognized arsenic and fluoride as the most severe inorganic contaminants in drinking water worldwide. Nitrate, primarily from agricultural runoff, is the most common chemical contaminant in the world's groundwater and can also cause health problems at relatively low concentrations.
The measurement of these contaminants is typically expressed in parts per million (ppm), parts per billion (ppb), or parts per trillion. These measurements signify that even at 'invisible' concentrations, certain chemicals can pose a real threat to human wellbeing. Regulatory bodies like the Environmental Protection Agency (EPA) establish Maximum Contaminant Levels (MCLs) for primary contaminants to manage these risks, and exceeding these levels can result in fines and penalties.