Multiple Stressor Effects of Radon and Phthalates in Children: Background Information and Future Research

Abstract

The present paper reviews available background information for studying multiple stressor effects of radon (²²²Rn) and phthalates in children and provides insights on future directions. In realistic situations, living organisms are collectively subjected to many environmental stressors, with the resultant effects being referred to as multiple stressor effects. Radon is a naturally occurring radioactive gas that can lead to lung cancers. On the other hand, phthalates are semi-volatile organic compounds widely applied as plasticizers to provide flexibility to plastic in consumer products. Links of phthalates to various health effects have been reported, including allergy and asthma. In the present review, the focus on indoor contaminants was due to their higher concentrations and to the higher indoor occupancy factor, while the focus on the pediatric population was due to their inherent sensitivity and their spending more time close to the floor. Two main future directions in studying multiple stressor effects of radon and phthalates in children were proposed. The first one was on computational modeling and micro-dosimetric studies, and the second one was on biological studies. In particular, dose-response relationship and effect-specific models for combined exposures to radon and phthalates would be necessary. The ideas and methodology behind such proposed research work are also applicable to studies on multiple stressor effects of collective exposures to other significant airborne contaminants, and to population groups other than children.

Keywords: children; dosimetric modeling; multiple stressor effects; phthalates; radon.

Figure 1

Multiple stressor effects on human beings caused by collective exposure to various significant airborne contaminants, e.g., radon progeny, phthalates, cigarette smoke, etc.

Figure 2

Multiple stressor effects from studies on combined effects of α-particles and depleted uranium (DU) on zebrafish (Danio rerio) embryos [15,16]. Conditions 1 to 4: [I_L] and [I_H] refer to low and high α-particle doses, respectively; [U_L] and [U_H] refer to low and high DU exposures, respectively. Circles: effects from individual stressors; crosses: effects from multiple stressors.

Figure 3

Structures of the ten widely used phthalates summarized by Wang et al. [73].

Figure 4

Typical differences in physiological parameters between the normal lung and the lung with obstruction in terms of inspiratory reserve volume (IRV), tidal volume (TV), expiratory reserve volume (ERV) and residual volume (RV) (adopted from [138]).

Figure 5

(a) Schematic diagram of radiation-induced bystander effect (RIBE). (b) Schematic diagram of radiation-induced rescue effect (RIRE). Irradiated cells are shown in green, and bystander cells in blue; bystander signals are shown as pink arrows and rescue signals as blue arrows.