Break point analyses of human or environmental temporal trends of POPs

The concentrations of a pollutant in people or in the environment are often changing as a function of time. In many cases, this rate of change may be relatively constant as a function of time; thus, first-order kinetics can be applied to these data. In other cases, the rate at which the concentrations of a pollutant are changing may be different before and after some event, for example before and after their regulation or usage restriction. This time is called a break point, and one needs to be able to determine this break point objectively before one can determine the rates of change on either side of it. This paper presents a method for doing this using the Solver feature of Excel followed by multiple linear regression to determine if the rates of change before and after the break point are statistically different from one another.