NON-CANCER HEALTH RISK ASSESSMENT FROM EXPOSURE TO CYANIDE BY RESIDENT ADULTS FROM THE MINING OPERATIONS OF BOGOSO GOLD LIMITED IN GHANA

Transcription

1 NON-CANCER HEALTH RISK ASSESSMENT FROM EXPOSURE TO CYANIDE BY RESIDENT ADULTS FROM THE MINING OPERATIONS OF BOGOSO GOLD LIMITED IN GHANA BY: S. OBIRI, D.K. DODOO, F. OKAI-SAM and D.K. ESSUNMANG EOH 2504: Principals of Environmental Exposure Class Paper Presentation Dolores Kirschner

2 Overview 1. Background A. Location B. Cyanide C. Cyanidation 2. Sampling Procedures 3. Risk Assessment A. Hazard Identification B. Exposure Assessment C. Toxicity Assessment D. Risk Characterization (Hazard Index) 4. Results 5. Conclusions 6. Limitations

3 1. Background A. Location: Ghana, Africa

4 1. Background B. Cyanide There are three main forms of cyanide found in mining effluents i. Free cyanide: *cyanide ion (CN - ) & *hydrogen cyanide (H + CN - ) ii. Weak dissociable cyanide: *metal-cyanide complex formed with the following metals zinc, cadmium and copper iii. Total Cyanide: *cyanide-metal complex formed with the following metals iron, gold and cobalt

5 1. Background C. Cyanidation Cyanidation recovery method can recover nearly 100% of the gold from its ore Profitable to process low-grade ores Gold is extracted from low-grade ore by the heap leaching method

6 1. Background C. Cyanidation Heap Leaching:

7 Mining companies & Regulators such as : Ghana Environmental Protection Agency, the Chamber of Mines & the Mines Department maintain cyanide breaks down quickly into less toxic forms (Note: The Government of Ghana owns 10% of the Bogoso/Prestea mine)

8 Contrary to claims the breakdown of cyanide is very slow The breakdown compounds: *Are potentially toxic to aquatic life *Can persist in the environment for long periods of time *Can be absorbed or bioaccumulate in plant, humans & aquatic organisms *Can also be absorbed by food crops grown in these areas

9 Purpose of Study: To evaluate the human health risk assessment of exposure to free cyanide via oral and dermal contact of surface/underground water by resident adults near Bogoso Gold Limited operations

10 2. Sampling Procedures Based on previous history of cyanide spills & visual assessment choose: -4 surface water sampling points *River Aprepre (River Dumasi) *Bogo River upstream *Bogo River downstream *River Ankobra -1 underground water sampling point *Boreholes (Dumasi)

11 2. Sampling Procedures Each sampling point had 32 total samples taken -8 samples each in 4 different zones Water samples from each sampling point were analyzed separately for free cyanide Then the mean results of free cyanide were computed for that sampling point

12 3. Risk Assessment A. Hazard Identification Cyanide *Limits absorption of oxygen *targets Central Nervous System Chronic symptoms seen in population near Bogoso Gold Limited Operations that are associated with cyanide ingestion: *headache, weakness, changes in sense of smell & taste, throat irritation, vomiting, nose bleeding, scarlet rashes, etc. Acute cyanide intoxication via ingestion and dermal contact results in poisoning, respiratory arrest and death all within a few minutes (many unexplained deaths have occurred after a cyanide spill)

13 3. Risk Assessment B. Exposure Assessment Only free cyanide was sampled Exposure scenario is a residential setting Ages of residential adults years Evaluated ingestion & dermal contact of surface water/ ground water by two parameters: CTE (Central Tendency Exposure) & RME (Reasonable Maximum Exposure)

14 3. Risk Assessment B. Exposure Assessment Intake of free cyanide from ingestion Intake = EPC x IR x EF x ED x 10 6 [mg/kg day] (BW x AT) EPC = EPC for free cyanide in water samples (mg/l) IR = ingestion rate of free cyanide in water samples (mg/day) EF = exposure frequency (day equivalents/year) ED = exposure duration (years) BW = body weight (kg) AT = averaging time (days)

15 3. Risk Assessment B. Exposure Assessment Intake of free cyanide from dermal contact Intake = (EPC x Kp x SA x EF x ED x 10-6 ) [mg/kg day] (BW x AT) EPC = EPC for free cyanide in water samples (mg/l) Kp = skin permeability constant SA = skin surface area EF = exposure frequency (day equivalents/year) ED = exposure duration (years) BW = body weight (kg) AT = averaging time (days)

16 3. Risk Assessment C. Toxicity Assessment For oral and dermal reference dose used US EPA online toxicity database file Default values from software Risc 4.02

17 3. Risk Assessment D. Risk Characterization Hazard index used to assess non-cancer health risks Hazard index: Compares estimated daily exposure dose of cyanide to the oral reference dose derived by the US EPA Hazard Index = Intake (mg/kg day) RfD (mg/kg day)

18 4. Results Most at risk for acute non-cancer health effects The chronic & subchronic risk of noncancer health effects are very small when compared with the acute toxic effects of cyanide

19 5. Conclusion After a cyanide spill communities whose source of drinking water has been contaminated should be provided with other sources of drinking water by the government and the mining companies Enforced regulation The public needs to be educated on symptoms of cyanide exposure & not to use the cyanidepolluted drinking water sources

20 6. Limitations NOT specified: *Type of sampling method used for surface or underground water samples *Time of year samples taken *Where each of the 4 sampling zones were for each sampling point *Raw data of the concentration of free cyanide in the samples from each sampling point (although recovery and reproducibility studies suggest a very efficient and reproducible method) Only 1 sampling point used for underground water Judgmental sampling technique