पर्यावरण एवं विश्लेषणात्मक विष विज्ञान

Trend Test and Change-Point Detection for Concentrations of I-131 in Drinking Water and Dairy Milk in the U.S. Midwest

Abstract

Alec Sithole*, Jones Mutua and Gwen Lack

Radioactive iodine (I-131) is one of the radionuclide byproducts of uranium and plutonium fission or neutron capture by Tellarium-130. I-131 decays to Xenon and releases β-particles and γ-radiation. Due to its release of IR during nuclear decay, I-131 is a potent radioactive hazard to public health. In this study, I-131 data from the EPA database, measured from drinking water and pasteurized dairy milk in the U.S. Midwest, were analyzed using non-parametric trend test and change-point detection techniques. We perform the Gaussian Kernel (G-K) smoothing to separate long-trends from the random noise in the data. The Mann-Kendall (M-K) rank correlation and Theil-Sen’s (T-S) tests indicated the existence of positive trends on the data. Furthermore, the Pettitt's Homogeneity (P-H) tests revealed statistically significant increases (α=0.05, p?0.0001) in I-131 radiation levels between the periods 1978-1983 and 1984-1990 in pasteurized dairy milk. With regards to drinking water, we noted significant increases between 1978-1995 and 1995-2017. We recommend further studies to determine the possible factors contributing to the periodicities in the data.