137Caesium, 40Potassium and potassium in raw and deep-oil stir-fried mushroom meals from Yunnan in China

A number of wild, edible mushroom species (Baorangia bicolor, Boletus calopus, Boletus obsclereumbrinus, Butyriboletus roseoflavus, Rubroboletus sinicus, Rugiboletus extremiorientalis and Xerocomus sp.) were collected in 2017, from Yunnan (Yuxi prefecture) in SW China. Samples of raw and stir-fried pools of these specimens were analysed for radioisotopes ¹³⁷Cs (caesium) and ⁴⁰K (potassium), and for total K concentrations. On a whole (wet) weight (ww) basis, ¹³⁷Cs activity ranged from < 0.10 to 0.75 Bq kg⁻¹ for raw, and from 0.5 to 4.4 Bq kg⁻¹ in stir-fried mushrooms. Radiopotassium (⁴⁰K) activity ranged from 57 to 96 Bq kg⁻¹ ww for raw, and 170 to 370 Bq kg⁻¹ ww for stir-fried mushrooms, while the corresponding concentration ranges for total K were 2100–3400 mg kg⁻¹ ww (mean: 2800 ± 3900 mg kg⁻¹ ww), and 6000–13000 mg kg⁻¹ ww-(mean: 8700 ± 2100 mg kg⁻¹ ww), respectively. This data indicates that mushrooms from this region show negligible ¹³⁷Cs contamination with evidently higher activity levels of ⁴⁰K. The deep oil stir-frying process results in enrichment in the resulting meals for all three determinants. 100 g meal portions showed ¹³⁷Cs activity in the range < 0.08 to 0.44 Bq 100 g⁻¹ ww (mean 0.15 ± 0.12 Bq 100 g⁻¹ ww), and ⁴⁰K activity from 16 to 37 Bq 100 g⁻¹ ww (mean 24 ± 6 Bq 100 g⁻¹ ww). The consequent exposure from ⁴⁰K contained in a single 100 g serving and weekly (100 g x7) servings was equivalent to radiation doses in the range of 0.099 to 0.23 μSv and 0.68–1.6 μSv per capita (means 0.15 ± 0.04 and 1.1 ± 0.3 μSv). This is equivalent to doses in the range of 0.0017 to 0.0038 μSv kg⁻¹ bm day⁻¹ and 0.011 to 0.027 μSv kg⁻¹ bm week⁻¹ respectively (mean values of 0.0025 ± 0.006 μSv kg⁻¹ bm day⁻¹and 0.018 ± 0.004 μSv kg⁻¹ bm week⁻¹). Analogically to the annual ¹³⁷Cs radiation exposure resulting from high rates of annual consumption (20–24 kg per capita), the estimated annual dose of radiation from ⁴⁰K would range from 0.34 up to 0.92 μSv kg⁻¹ bm (mean 0.60 μSv kg⁻¹ bm). Thus in practice, high annual consumption rates of wild, stir-fried mushrooms as seen in Yunnan, would result in negligible internal doses from decay of artificial ¹³⁷Cs, relative to that from natural ⁴⁰K. The 100 g servings also contained between 590–1300 mg K making this local food one of the top dietary sources of nutritionally important potassium for local consumers.