Natural radioactivity in soils of Ijero, Nigeria: measurements and risk assessment

Bailey, Tarryn (2019-12)

Thesis (MSc)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Several soil samples were obtained from Ijero, Nigeria, where the chemical and radio-toxicity of soil is under question due to ongoing and unregulated mining activities. The soil samples were crushed, sieved, dried and sealed in identical cylindrical containers. The activity concentrations of primordial radionuclides in the 238U series, 232Th series and 40K were measured using a High-Purity Germanium (HPGe) detector. Subsequently, radiological risk factors were calculated to assess the average risk to an individual living in Ijero. The measured activity concentrations for the 238U series ranged from 10.1 1.4 to 83.9 2.1 Bq/kg with a mean value of 38.5 Bq/kg. For the 232Th series, the activity concentrations ranged from 11.3 2.9 to 108.0 2.4 Bq/kg with a mean value of 37.1 Bq/kg. Finally, the 40K activity concentration ranged from 67 26 to 1196 36 Bq/kg with a mean value of 461 Bq/kg. The mean values for the activity concentrations of the 238U series, 232Th series and 40K were comparable to the global population-weighted average for concentration in soils, given by UNSCEAR 2000, of 33 Bq/kg, 45 Bq/kg and 420 Bq/kg respectively. In total, thirty soil samples from Nigeria were measured. Of these samples, thirteen had 238U series concentrations above 33 Bq/kg, three of those samples had activity concentrations for the 238U series above 70 Bq/kg. For the 232Th series, thirteen samples had activity concentrations above 45 Bq/kg with two samples above 90 Bq/kg. Finally, seventeen samples had 40K activity concentrations above 420 Bq/kg with eleven of those above 800 Bq/kg. Five soil samples had hazard indices that summed to more than the permissible limit of 1 mSv/yr. Eight samples were above the permissible limit for the Annual E ective Dose rate, where indoor and outdoor dose rates must sum to 1 mSv/yr. The Annual Gonadal Equivalent Dose limit of 300 Sv/yr was surpassed by twenty- ve samples. For the Excess Lifetime Cancer Risk (ELCR) and excess percentage risk, which estimates the probability that an individual could develop cancer in their lifetime, seven samples exceeded the maximum ELCR of 0:29 10􀀀3. The ELCR results ranged from 0:102 10􀀀3 to 0:483 10􀀀3. The highest ELCR result is 1.67 times greater than the upper recommended value of 0:29 10􀀀3. A value of 1.67 for the ratio of the calculated ELCR to the maximum permissible ELCR corresponds to an excess percentage risk of 67%. The mean ELCR is 0:239 10􀀀3 which is below the maximum recommended value. There are certain locations where the activity concentration of primordial radionuclides is high, far surpassing the world average. However, most of the soil samples measured did not exceed the recommended maxima for activity concentrations and radiological risk factors.

AFRIKAANSE OPSOMMING: Verskeie grondmonsters is verkry uit Ijero, Nigeri e, waar die chemiese en radiotoksisiteit van grond bevraagteken word weens voortgesette en ongereguleerde mynaktiwiteite. Die grondmonsters is fyngedruk, gesif, gedroog en in identiese silindriese houers verse el. Die aktiwiteitskonsentrasies van oer-radionukliede in die 238U-reeks, 232Th-reeks en 40K is gemeet met behulp van 'n Ho e Suiwerheid Germanium (HPGe) detektor gekoppel aan 'n Palmtop multikanaal-ontleder (MCA). Daarna is radiologiese risikofaktore bereken om die risiko gemiddelde vir 'n individu wat in Ijero woon te bepaal. Die gemete aktiwiteitskonsentrasies vir die 238U-reeks het gewissel van 10.1 1.4 tot 83.9 2.1 Bq/kg met 'n gemiddelde waarde van 38.5 Bq/kg. Vir die 232Threeks het die aktiwiteitskonsentrasies gewissel van 11.3 2.9 tot 108.0 2.4 Bq/kg met 'n gemiddelde waarde van 37.1 Bq/kg. Laastens het die 40K aktiwiteitskonsentrasie gewissel van 67 26 tot 1196 36 Bq/kg met 'n gemiddelde waarde van 461 Bq/kg. Die gemiddelde waardes vir die aktiwiteitskonsentrasies van die 238U-reeks, 232Th-reeks en 40K was vergelykbaar met die w^ereldwye bevolkingsgeweegde gemiddelde vir konsentrasie in grondsoorte, gegee deur UNSCEAR 2000, van onderskeidelik 33 Bq/kg, 45 Bq/kg en 420 Bq/kg. 'n Totaal van dertig grondmonsters uit Nigeri e is gemeet. Hieruit was die 238Ureeks konsentrasies van dertien monsters bo 33 Bq/kg. Drie van die monsters het aktiwiteitskonsentrasies vir die 238U-reeks bo 70 Bq/kg gehad. Vir die 232Threeks het dertien monsters aktiwiteitskonsentrasies bo 45 Bq/kg gehad met twee monsters bo 90 Bq/kg. Die 40K aktiwiteitskonsentrasies van sewentien monsters was bo 420 Bq/kg, met elf hiervan meer as 800 Bq/kg. Vyf grondmonsters het gevaarindekse gehad wat tot meer as die toelaatbare limiet van 1 mSv/jr saamgestel het. Agt monsters was bo die toelaatbare limiet vir die jaarlikse e ektiewe dosis tempo, waar binne en buite dosis tempo's tot 1 mSv/jr moet saamtel. Die jaarlikse gonadale ekwivalente dosisgrens van 300 Sv/jr is oorskry deur vyf en twintig monsters. Vir die oormaat leeftyd kankerrisiko (ELCR) en die oormaat persentasierisiko, wat die waarskynlikheid dat 'n individu kanker kan ontwikkel in hul leeftyd beraam, het sewe monsters die maksimum ELCR van 0:29 10􀀀3 oorskry. Die ELCR resultate het gewissel van 0:102 10􀀀3 tot 0:483 10􀀀3. Die hoogste ELCR resultaat is 1.67 keer groter as die boonste aanbevole waarde van 0:29 10􀀀3.'n Waarde van 1.67 vir die verhouding van die berekende ELCR tot die maksimum toelaatbare ELCR stem ooreen met 'n oortollige persentasie risiko van 67%. Die gemiddelde ELCR is 0:239 10􀀀3, wat onder die maksimum aanbevole waarde is. Daar is sekere plekke waar die aktiwiteitskonsentrasie van oer-radionukliede hoog is, wat die w^ereldgemiddelde ver oortref. Die meeste grondmonsters wat gemeet is het egter nie die aanbevole maksimum vir aktiwiteitskonsentrasies en radiologiese risikofaktore oorskry nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107225
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