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Hydrochemical investigation and socioeconomic assessment in Rio Zapomeca river basin focusing on arsenic contamination

Rydstedt, Anton LU and Hagström, Axel (2015) In ISRN VTG820 20151
Engineering Geology
Civil Engineering
Abstract
The awareness of problems concerning arsenic contaminated drinking water sources has during recent years increased. WHO (World Health Organization) decided in 1993 to lower the recommended limit of arsenic in drinking water from 50 μg/l to 10 μg/l, mainly due to observations of its carcinogenicity. New places where the WHO limit for arsenic is exceeded are constantly discovered all over the world. Several areas in Nicaragua in Central America have since 1996 been discovered to have arsenic concentrations above the recommendations.

This Minor Field Study aims to investigate the origin and triggers of the arsenic that is contaminating the drinking water sources in the river basin of Rio Zapomeca located in central Nicaragua. The study... (More)
The awareness of problems concerning arsenic contaminated drinking water sources has during recent years increased. WHO (World Health Organization) decided in 1993 to lower the recommended limit of arsenic in drinking water from 50 μg/l to 10 μg/l, mainly due to observations of its carcinogenicity. New places where the WHO limit for arsenic is exceeded are constantly discovered all over the world. Several areas in Nicaragua in Central America have since 1996 been discovered to have arsenic concentrations above the recommendations.

This Minor Field Study aims to investigate the origin and triggers of the arsenic that is contaminating the drinking water sources in the river basin of Rio Zapomeca located in central Nicaragua. The study also evaluates different drinking water distribution methods and assesses the need of arsenic filters, so called Kanchan filters, by doing an analysis according to the principles of cost-benefit-analysis.

Nicaragua is located close to a subduction zone resulting in tectonically active geology including earthquakes, active volcanoes and geothermal activity. The river basin of Rio Zapomeca is no exception with both hot springs and strong faulting. The geology in the river basin is dominated by two Tertiary groups named Matagalpa and Coyol. This study includes hydrochemical measurements of pH, temperature, salinity, conductivity and total dissolved solids. Arsenic analysis of drinking water sources and collected rock samples were also carried out. Furthermore, resistivity surveys and groundwater level measurements were done.

The arsenic analysis showed that 15 of the 20 analysed drinking water samples had an arsenic concentration above the WHO limit (10 μg/l). The highest value of 104 μg/l was found in Los Negritos. The results of the investigations showed that the correlation between arsenic and the hydrochemical parameters pH, temperature, salinity and total dissolved solids is weak. The correlation with conductivity the highest showing an R2-value of 0.47. The decrease of arsenic in relation to increase of elevation shows a clear trend in the project area but the reason is unclear, perhaps the increased elevation results in shorter retention time due to higher hydraulic gradient and thereby less time to dissolve arsenic. The clearest connection found is that elevated values of arsenic, both in the rock samples and in the water, occur along the contact zone between the rock type groups Coyol and Matagalpa in the southern to south-western part of the Zapomeca basin. The geothermal activity does probably affect the arsenic concentration in the groundwater, since the solubility of arsenic in water increases with temperature. However, to conclude the geothermal involvement concerning the arsenic contamination in the river basin of Rio Zapomeca further studies are needed.

The decrease in life expectancy for persons living in the river basin of Rio Zapomeca due to drinking the arsenic contaminated water was calculated using two different methods. The first method which included calculations regarding the percentage of life reduced resulted in an average decreased life expectancy of 3.2 years. The second method was calculated with the relative risk methodology that 26% of the deaths in the river basin can be linked to arsenic contaminated drinking water. Assuming that each person that dies of arsenic contaminated drinking water loses 15 years of lifetime makes the life expectancy decreases with 3.9 years. The value of statistical life (VSL) of a Nicaraguan was estimated to a value of $260 000. By using the VSL it was proven that it is economically valid to invest in Kanchan filters for the population living in the Rio Zapomeca river basin. The payback for each dollar invested varies depending on which discount rate that is used. Calculating conservatively and with a high but reasonable discount rate the payback per invested dollar is at least $2.6 thus making it a sound investment. (Less)
Popular Abstract (Swedish)
Undersökning och hantering av arsenikförorenade brunnar i Nicaragua

Arsenik förorenar dricksvatten i Nicaragua och framkallar cancer. Lösningen är enkel: sand, tegelstenar och järnspikar.

Varje år dör hundratusentals människor till följd av arsenikförorenat dricksvatten. Världshälsoorganisationen WHO listar arsenik på topp-tio-listan över de kemikalier i världen som hotar människors hälsa mest. Hela tiden upptäcks nya områden där arsenikföroreningarna utgör en stor risk för befolkningen.

Den här studien är gjord i floden Rio Zapomecas avrinningsområde i Nicaragua i Centralamerika. Området ligger långt ifrån större städer och är ett av landets fattigaste, med svår torka varje år och dålig vattentillgång. Under studien testades... (More)
Undersökning och hantering av arsenikförorenade brunnar i Nicaragua

Arsenik förorenar dricksvatten i Nicaragua och framkallar cancer. Lösningen är enkel: sand, tegelstenar och järnspikar.

Varje år dör hundratusentals människor till följd av arsenikförorenat dricksvatten. Världshälsoorganisationen WHO listar arsenik på topp-tio-listan över de kemikalier i världen som hotar människors hälsa mest. Hela tiden upptäcks nya områden där arsenikföroreningarna utgör en stor risk för befolkningen.

Den här studien är gjord i floden Rio Zapomecas avrinningsområde i Nicaragua i Centralamerika. Området ligger långt ifrån större städer och är ett av landets fattigaste, med svår torka varje år och dålig vattentillgång. Under studien testades arsenikhalten i 20 brunnar och källor och i 15 av dessa visade sig arsenikhalten överstiga WHOs rekommenderade värde på 10μg/l. Det högsta värdet i området låg på 104 μg/l, alltså mer än tio gånger högre än WHOs rekommenderade värde. I de sex byar med högst arsenikkoncentration inom studieområdet beräknas 1.8 personer dö varje år på grund av att ha druckit arsenikförorenat vatten.

Orsaken eller orsakerna bakom arsenikföroreningarna i området kring Rio Zapomeca är svåra att förklara, men med stor sannolikhet kommer de ifrån berggrunden i området. För att arsenik ska hamna i grundvattnet räcker det inte med att det finns i berggrunden, det måste finnas något som gör att arsenik löser sig i vattnet också, en så kallad “trigger”. Vanliga “triggers” kan vara reducerande förhållanden eller höga grundvattentemperaturer. I området kring Rio Zapomeca finns flera varma källor och en av teorierna kring orsaken bakom arsenikföroreningarna är just dessa varma källor. Arsenik löser sig nämligen lättare i varmare vatten än kallt. Det tydligaste sambandet som hittades under studien var att arsenikhalten i dricksvattnet minskade ju högre upp i landskapet man kommer. De norra delarna av området ligger flera hundra meter högre och terrängen är bergigare och brantare än i den flackare floddalen. De högsta arsenikhalterna finns just i floddalen medan de lägsta finns längre norrut. Antagligen beror detta på att grundvattnet stannar kvar längre i floddalen och då får arseniken längre tid på sig att lösa sig.

Ett sätt att komma tillrätta med föroreningarna kan vara att installera filter. Forskare vid Massachusetts Institute of Technology (MIT) har tagit fram ett arsenikfilter som är både enkelt och effektivt. Filtret har fått namnet Kanchan och har använts världen över och räddat ett oräkneligt antal liv. Enligt cost-benefit-analysen som gjordes i den här studien, har samhällena kring Rio Zapomeca mycket att vinna på att köpa in Kanchan-filtret. Filtret är billigt och lätt att sköta och består faktiskt bara av sand, grus, tegelsten, järnspikar och en hink med tapp. I cost-benefit-analysen tas också det statistiska värdet på en person (Value of Statistical Life) i Nicaragua fram, vilket resulterar i $260 000. Det kan jämföras med Sverige där det ligger på $ 2.6 miljoner.

Om du vill läsa mer om det här så går rapporten av Axel Hagström och Anton Rydstedt att finna på institutionerna Teknisk Geologi och Riskhantering vid Lunds Tekniska Högskola. "A hydrochemical investigation and risk assessment in Rio Zapomeca river basin focusing on arsenic contamination" (Less)
Please use this url to cite or link to this publication:
author
Rydstedt, Anton LU and Hagström, Axel
supervisor
organization
alternative title
Undersökning och hantering av arsenikföroreningar vid Rio Zapomeca i Nicaragua
course
VTG820 20151
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
water pollution, Kanchan filter, value of statistical life, cost-benefit-analysis, socioeconomic, premature mortality, resistivity, risk, groundwater, Nicaragua, geology, Arsenic
publication/series
ISRN
report number
5143 & 5011
other publication id
LUTVDG/TVRH--(5011)—SE
LUTVDG/(TVTG--5143)/1-85/(2015)
language
English
id
8229364
date added to LUP
2015-12-01 13:13:05
date last changed
2015-12-01 13:13:05
@misc{8229364,
  abstract     = {The awareness of problems concerning arsenic contaminated drinking water sources has during recent years increased. WHO (World Health Organization) decided in 1993 to lower the recommended limit of arsenic in drinking water from 50 μg/l to 10 μg/l, mainly due to observations of its carcinogenicity. New places where the WHO limit for arsenic is exceeded are constantly discovered all over the world. Several areas in Nicaragua in Central America have since 1996 been discovered to have arsenic concentrations above the recommendations.

This Minor Field Study aims to investigate the origin and triggers of the arsenic that is contaminating the drinking water sources in the river basin of Rio Zapomeca located in central Nicaragua. The study also evaluates different drinking water distribution methods and assesses the need of arsenic filters, so called Kanchan filters, by doing an analysis according to the principles of cost-benefit-analysis.

Nicaragua is located close to a subduction zone resulting in tectonically active geology including earthquakes, active volcanoes and geothermal activity. The river basin of Rio Zapomeca is no exception with both hot springs and strong faulting. The geology in the river basin is dominated by two Tertiary groups named Matagalpa and Coyol. This study includes hydrochemical measurements of pH, temperature, salinity, conductivity and total dissolved solids. Arsenic analysis of drinking water sources and collected rock samples were also carried out. Furthermore, resistivity surveys and groundwater level measurements were done.

The arsenic analysis showed that 15 of the 20 analysed drinking water samples had an arsenic concentration above the WHO limit (10 μg/l). The highest value of 104 μg/l was found in Los Negritos. The results of the investigations showed that the correlation between arsenic and the hydrochemical parameters pH, temperature, salinity and total dissolved solids is weak. The correlation with conductivity the highest showing an R2-value of 0.47. The decrease of arsenic in relation to increase of elevation shows a clear trend in the project area but the reason is unclear, perhaps the increased elevation results in shorter retention time due to higher hydraulic gradient and thereby less time to dissolve arsenic. The clearest connection found is that elevated values of arsenic, both in the rock samples and in the water, occur along the contact zone between the rock type groups Coyol and Matagalpa in the southern to south-western part of the Zapomeca basin. The geothermal activity does probably affect the arsenic concentration in the groundwater, since the solubility of arsenic in water increases with temperature. However, to conclude the geothermal involvement concerning the arsenic contamination in the river basin of Rio Zapomeca further studies are needed.

The decrease in life expectancy for persons living in the river basin of Rio Zapomeca due to drinking the arsenic contaminated water was calculated using two different methods. The first method which included calculations regarding the percentage of life reduced resulted in an average decreased life expectancy of 3.2 years. The second method was calculated with the relative risk methodology that 26% of the deaths in the river basin can be linked to arsenic contaminated drinking water. Assuming that each person that dies of arsenic contaminated drinking water loses 15 years of lifetime makes the life expectancy decreases with 3.9 years. The value of statistical life (VSL) of a Nicaraguan was estimated to a value of $260 000. By using the VSL it was proven that it is economically valid to invest in Kanchan filters for the population living in the Rio Zapomeca river basin. The payback for each dollar invested varies depending on which discount rate that is used. Calculating conservatively and with a high but reasonable discount rate the payback per invested dollar is at least $2.6 thus making it a sound investment.},
  author       = {Rydstedt, Anton and Hagström, Axel},
  keyword      = {water pollution,Kanchan filter,value of statistical life,cost-benefit-analysis,socioeconomic,premature mortality,resistivity,risk,groundwater,Nicaragua,geology,Arsenic},
  language     = {eng},
  note         = {Student Paper},
  series       = {ISRN},
  title        = {Hydrochemical investigation and socioeconomic assessment in Rio Zapomeca river basin focusing on arsenic contamination},
  year         = {2015},
}