Calculating the Lowest Reportable Concentrations of Toxic Chemicals in the Environment

The equation promulgated by 40 Code of Federal Regulations (CFR) to calculate method detection limit (MDL) and used since 1981 in the United States and other countries to protect public health and the environment is incorrect. As a result, toxic chemicals in a large number of air, food, water, wastes, and other environmental samples may in fact be present at measurable concentrations even though they are currently being reported as “not detected”. That is, the air we breathe, the food we eat, and the water and other liquids we drink may have measurable concentrations of toxic chemicals, despite being reported as not detected and assumed to be absent. Furthermore, many chemicals, such as arsenic (As) in drinking water, are so toxic that they cannot be measured to safe levels and the allowable limits must be set at the lowest reportable concentrations. As a result, the allowable limits for some extremely toxic chemicals may be incorrectly set too high. Therefore, the consequences of this error pose a risk to public health and the environment. The sources of this error are explained and two improved ways of calculating method detection limit are presented.