The use of radio-nuclides (unsupported 210Pb, 7Be and 137Cs) in air, rain and undisturbed soil as environmental tools

• Main Author: Choubedar, Feraidoun
• Published: University of Edinburgh 2000
• Subjects: 577.14
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.643140

Soil inventories of atmospherically derived ²¹⁰Pb (radioactive half lives 22.3 years) were used to determine deposition patterns of atmospherically derived aerosols averaged over decades at low altitude sites (51-6° N, 0.6° W) and quantify the enhancement in aerosol deposition by aerodynamically rough canopies (forest) relative to short vegetation (grass). ²¹⁰Pb and ⁷Be (radioactive half life 53.4 days) in surface air and rain (55.6° N, 3.9° W) were measured to determine the concentration of these radionuclide isotopes in the environment. Non-destructive gamma-spectrometry was used for all 3 parts using high purity germanium (HPGe) detectors. From the soil samples ¹³⁷Cs (radioactive half life 30.2 years) are being measured and reported. The average inventories to the canopies compared to the short vegetation for ²¹⁰Pb and ¹³⁷Cs for Geescroft forest were 25.7% and 60.8% higher than the open field inventories, respectively; the corresponding values for Broadbalk forest were 30.9% and 68.9% for ²¹⁰Pb and ¹³⁷Cs, respectively. Although these two forests are not far from each other and have the same altitude, the excess inventories for Broadbalk forest are larger than Geescroft forest and this could be due to the fact that this forest is acting as an edge, because of its width. The averaged flux for Rothamsted forest soils for ²¹⁰Pb was determined as 211 ± 6 Bq m^-2 y^-1 per metre of rainfall, and for the soil and vegetation in the open area 167 ± 6 Bq m^-2 y^-1 per metre of rainfall. The annual average concentrations in surface air were 0.19 ± 0.06 and 2.71 ± 0.66 mBq m^-3 for ²¹⁰Pb and ⁷Be, respectively. The annual fluxes of ²¹⁰Pb and ⁷Be in rain were determined as 68 ± 10 and 787 ± 29 Bq m^-2 y^-1 per metre of rainfall, respectively. There was a seasonal variation for ⁷Be concentrations in air and rain giving spring high. The highest concentrations for ²¹⁰Pb were obtained when the air mass origin was from continent. From the air and rain data for ²¹⁰Pb and ⁷Be, similar washout scavenging ratios (W_s) were obtained, indicating they are scavenged from the atmosphere with a similar rate. The dry deposition of ²¹⁰Pb and ⁷Be carrier aerosols were estimated as 41 ± 13% and 35 ± 9% of the total deposition for ²¹⁰Pb and ⁷Be, respectively.