Risk Assessment of Exposure to Natural Radiation in Soil Using RESRAD-ONSITE and RESRAD-BIOTA in the Cobalt-Nickel Bearing Areas of Lomié in Eastern Cameroon

Abstract

Nkamouna-Kongo is a cobalt–nickel deposit located in Lomié, Eastern Cameroon. Mining creates radiation exposure pathways that must be considered in risk management scenarios. RESRAD-ONSITE and RESRAD-BIOTA, developed by the US DOE, assess contaminated sites by deriving cleanup criteria and estimating the radiation dose and risk associated with residual radioactive materials using site-specific parameters. This paper evaluated the radiation dose in biota and the health risk from exposure to naturally occurring radionuclides. The activity of 226Ra, 232Th, and 40K was determined by γ-spectrometry. The internal doses were 2.13 × 10−07, 1.42 × 10−06, and 8.38 × 10−05 Gy d−1 for animals and 2.38 × 10−07, 2.04 × 10−06, and 9.07 × 10−05 Gy d−1 for plants. The maximum total dose of 0.7234 mSv yr−1 was obtained at t = 1 year. The external dose contribution obtained at t = 1 year for all nuclides summed and all component pathways was 0.4 mSv yr−1, above the background radiation dose limit of 2.5 × 10−01 mSv yr−1. A maximum cancer risk of 1.36 × 10−03 was observed at t = 1 year. It was also shown in the RESRAD calculations that the total cancer morbidity risks from plant ingestion, radon (independent of water), and external gamma exposure pathways were greater than those from other exposure pathways. The high risk calculated for 226Ra relative to 232Th and 40K makes it the primary human health concern in the study area. The use of a 1 m cover thickness would remediate the contaminated site to a dose on the order of 10−5 mSv yr−1 for a period of 0 to 100 years. The values of these doses are below the US DOE recommended limits.