Environmental Radiation and Human Health: From Radon to the Sun

Abstract

Environmental radiation, often referred to as “background radiation”, is around us all the time. There are three main natural sources of environmental radiation: cosmic radiation that comes from the sun and stars, terrestrial radiation that comes from the Earth’s radioactive materials, and internal radiation from inside human bodies. Background radiation, though presented at low level, is continuous, ubiquitous, and established to have negative impact on multiple human health outcomes. This dissertation focused on the main components of the first two types of radiation sources, applying statistical methods to investigate their characteristics and health effects as public health exposure. In the first study of this dissertation, we established a novel method to study a new type of exposure, particle radioactivity (PR), which comes from the attachment of radionuclides on surfaces of particulate matters (PM). The biggest contribution of radiation in natural environment is radon (222Radon) and its decay products, and we proposed that PR from these radionuclides is responsible for part of PM toxicity. Based on the daily ambient PM2.5 and PM10 filters collected at Harvard Supersite in downtown Boston, Massachusetts, we developed a method to back calculate the actual level of α and β activity on the PM filters that time of sample collection. We found strong contribution from PM2.5 radioactivity to the total PM10 radioactivity, and we obtained good consistency between our measurements and measurements from the RadNet system of the US EPA. Based on the method developed in the first study, we took one step further from the ambient environment to indoor environment. People nowadays spend most of their time indoor, but few study has investigated the factors contributing to indoor radiation levels related with particles. Using the PM2.5 filters collected from homes of COPD patients living in Eastern Massachusetts as well as from Harvard Supersite, we were able to identify that ambient PM2.5 α activity from long-lived radon decay products is a strong contributor to that of indoor environment. Residential radon, air infiltration between indoor and ambient, as well as several other residential factors are also related with indoor PM2.5 α activity at lower magnitude. In the third study of this dissertation, we focused on the radiation from the sun, particularly three parameters that reflect solar activity from different aspects: strength of interplanetary magnetic field (IMF) carried out by the solar plasma, Kp index that represents the level of geomagnetic disturbance caused by the interaction between IMF and geomagnetic field, and sunspot number that directly reflects strength of solar activity. We investigated their impact on gestational age at delivery among neonates born in Massachusetts from 2001-2015 using causal modeling method. This analysis demonstrated that higher level of solar and geomagnetic activity reduces expected gestational age and consequently increases percentage of preterm birth in the population.