What is the relationship between 1 mg/L and ppm?

1 mg/L is equivalent to 1 ppm (parts per million) because both measurements represent a ratio of mass to volume in a liquid solution, specifically in water. The relationship stems from the definition of ppm, which is often used in environmental science to express very dilute concentrations. When dealing with water, 1 liter of water weighs approximately 1,000 grams. Therefore, 1 mg of a substance in 1 liter of water results in a concentration of 1 mg per 1,000,000 mg, which simplifies to 1 ppm. This direct correlation makes it easy to translate between milligrams per liter and parts per million when the density of the solution is similar to that of water.