Comparison between EPA UV index app and UV monitor to assess risk for solar ultraviolet radiation exposure in agricultural settings in Eastern North Carolina

Agricultural workers are exposed to solar ultraviolet (UV) radiation due to the significant amount of time spent working outdoors. Risk information on UV exposure from the EPA SunWise UV Index mobile app is conveniently available for timely advice on risk management, but its reliability is unknown. The purpose of this study was to determine the reliability of the EPA UV Index app in providing accurate risk information to reduce UV exposure and prevent related illnesses among agricultural workers in eastern North Carolina. UV radiation effective irradiance (UVeff) indices were datalogged at two agricultural sites using radiometers from April-August 2019 and were assigned to risk levels (low, moderate, high, very high, extreme) based on the ACGIHVR Threshold Limit Values (TLVsVR). The UV index (UVapp) and its corresponding risk level were obtained using the app. Hourly UVapp-based risk level assignments were time-matched to their corresponding UVeff/TLV-based risk level assignments (871 pairs) and analyzed using cross tabulation by determining the percentage of hourly UVeff/TLV-based risk levels ("gold standard") with the same hourly UVapp-based risk levels, with a larger percentage indicating higher app reliability. Results showed that the app correctly identified 100% of low risk conditions, but its reliability decreased as the UV risk condition became more severe. The app correctly identified 0% of moderate, high and very high risk conditions but instead assigned 100% of them to lower risk levels (30-100% as low risk, 5-70% as moderate risk), indicating that the app was less protective in assessing UV risk. The app correctly identified 0.6% of extreme risk conditions but assigned 99.4% of them to lower risk levels (9.4% as low, 29.7% as moderate, 24.6% as high, 35.8% as very high). It is concluded that the performance of the EPA UV Index app in assessing occupational UV risk is not protective of workers particularly for high risk conditions, and that the use of the app for the assessment of risk to UV exposure in agricultural settings is not recommended.