Richard Couture.Natural Resources Canada [email protected]
J.D.Lambert.Fisheries and Oceans Canada [email protected]
August 21 2003. GGMC Mining Week. Le Méridien Pegasus, Georgetown, Guyana
Source of mercury in mining communities of Guyana.
Background Modern gold rush started in the late 1970’s;
Mercury release estimates by Malm (1998), Pfeiffer and Lacerda (1988) and
Pfeiffer et al. (1993);
Environmental consequences of Hg; amalgamation mining on the tropical ecosystems of South America began in the mid- to late-
1980s (Pfeiffer and Lacerda, 1988; Martinelli et al., 1988; Lacerda et al., 1989, 1990;
1991a, 1991b; Malm et al. 1990; Pfeiffer et al., 1989, 1991; Lacerda and Salomons, 1992;
Nriagu et al., 1992);
Other source of Hg to the aquatic environment on a regional scale:
1. Hg concentrations in no known mining areas exhibit values on a
regional scale that are comparable to those in basins with extensive
mining operations (Forsberg et al., 1995; Malm, 1998; Roulet et al. 1998);
2. Hg concentrations do not systematically decrease downstream of the
mining camps as expected from point sources of contamination(Lechler et al., 2000; Roulet et al., 1998);
Objectives of the study
1. Provide measurements of mercury from amalgam mining areas and from areas of no-known modern mining activity;
2. Investigate if mercury manipulation during the gold amalgamation process can be link to the mercury found in the aquatic environment.
Sampling programme
Methyl-mercury in:
– Fish (80 samples)
Total-mercury in:
– Water (350 samples)
– Riverbed sediments (400)
– Land sediments (100)
– Fish (1 200)
Study sites
•Lower Potaro River
•Upper Potaro River
•Lower Essequibo River
•Upper Essequibo River
•Kamarang River
•Mazaruni River
•Kurupung River
•Barima River
•Multiple Creeks
Results – Objective 1
Hg in water:– Typical water column vertical distribution shows Hg
peak concentration at 1m depth in all mining and non-mining areas;
– The similar trend between turbidity and Hg in unfiltered water suggests equivalent [Hg]/sediment load for mining and non-mining areas.
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
10,0
0 500 1000 1500 2000 2500
T-Hg (ng/L)
Dep
th (
m)
Hg and Turbidity in unfiltered water
0
10
20
30
40
50
60
70
80
90
100
L_Potaro Barima U_Essequibo U_Potaro Kamarang
River
Tu
rbid
ity (
NT
U)
0
100
200
300
400
500
600
700
Hg
(n
g/L
)
Hg
Turbidity
Results – Objective 1 Hg in riverbed sediments:
– 90% of Hg is associated with mud;
– Low [Hg] variability in the mud fraction between mining or non-mining areas;
– Thin mud layer on the riverbed which is more extended downstream mining creeks than upstream and than in non-mining areas.
Hg in riverbed sediments
0
20
40
60
80
100
120
140
160
180
Mud Mud+Sand Sand Sand+Gravel
Hg
(n
g/g
)
Mercury in Potaro Riverbed sediments
0
50
100
150
200
250
300
350
Amatuk Mahdia Konawak Tiger
Lower Potaro River
Hg
(n
g/g
) Amatuk
FallsMadia Cr.
INPUT
Kuribrong
INPUT
SS
SS
S
S
SS
S
SSS
SS
S
S
- Classified as mud
- Classified as sand
S
Results – Objective 1
Hg in land sediments:– 90% Hg is associated with mud;
– Low [Hg] variability in the mud fraction between mining or non-mining areas;
– Peak mud abundance found in the overburden;
– Comparable profiles in pristine and mining areas.
Hg in land sediments
0
20
40
60
80
100
120
140
160
180
mud sand+mud sand sand+gravel
Hg
(n
g/g
)
Vertical profiles of land sediments
0
1
2
3
4
5
0 50 100 150 200 250 300 350 400 450 500
Hg (ng/g)
Dep
th (
m)
Gunn'FiveStar
Results – Objective 1
Hg in fish:– 90% T-Hg is in the form of Me-
Hg;
– Mining areas show highest Hg levels in carnivorous fish;
– Omnivorous and herbivorous fish are below 0,5μg Hg/g (WHO) in mining and non-mining areas.
Regression MeHg / T-Hg
MeHg = 0,8928 T-Hg + 0,0362
R2 = 0,9833
0
1
2
3
4
0 1 2 3 4
T-Hg µg/g
MeH
g µ
g/g
Hg in fish flesh
0,0
0,2
0,4
0,6
0,8
1,0
1,2
Mazaruni Kurupung Potaro Barima Essequibo Kamarang
River
ug
Hg
/
Carnivorous
Omnivorous
Herbivorous
0,5μg Hg/g
Results –
Objective 2
Source of Hg– Irrespective of the sampling area
(mining or non-mining), [Hg] is
related to size class of substrat;
– Irrespective of the sampling area
(mining or non-mining) [Hg] is
the same on land and on
riverbeds;
– As showed from the Potaro river
riverbed sediment study, the
extension of the mud layer on the
riverbed is greater downstream
mining creeks.
Hg in land sediments
146
59
4
9
0
20
40
60
80
100
120
140
160
180
Hg
(n
g/g
)
Hg in riverbed sediments
141
66
126
0
20
40
60
80
100
120
140
160
180
Mud Mud+Sand Sand Sand+Gravel
Hg
(n
g/g
)
Results –
Objective 2
Source of Hg– On land sediments, average
concentration of Hg from all
size classes is not mining
related.
– On riverbed sediments,
average Hg concentration for
all size classes shows that
mining areas contain more Hg
(mud) than from non-mining
areas;
Hg in riverbed sediments
0
50
100
150
200
250
300
Min
ing
Cre
eks
Maz
arun
i
Lower
Pot
aro
Lower
Ess
equib
o
Bar
ima
Pris
tine
Cre
eks
Uppe
r Ess
equib
o
Uppe
r Pot
aro
Kam
arang
Hg
(n
g/g
)
Hg in land sediments
0
20
40
60
80
100
120
140
160
180
Mazaruni Arakaka Upper-
Essequibo
Kamarang FiveStar Lower-
Essequibo
White Hole
(Potaro)
Hg
(n
g/g
)
Results –
Objective 2
Source of Hg– On the riverbed of the Potaro River
and in the White Hole mine facing
Region 9), the most abundant
fraction of Hg is associated with
humic organic matter;
– In the White Hole mine facing,
this fraction is located in the
overburden.
Hg in the Potaro riverbed sediments
0
20
40
60
80
100
120
140
160
180
Mahdia Konawak Tiger
Lower-Potaro
Hg
(n
g/g
)
F0
F1
F2
F3
F4
F5
White Hole Mine Facing
0 20 40 60 80 100
0
2
4
8
11
Dep
th (
m)
Hg (ng/g)
F0=Free liquid Hg
F1=Water soluble Hg
F2=Acid soluble Hg
F3=Humic associated
Hg
F4=Non-humic bound
HgII
F5=Amalgam Hg with
gold & platinum
Conclusion Objective 1:
– Hg is trapped in the mud fraction over all land areas but on the
riverbeds it is concentrated downstream from mining activities;
– Me-Hg exceeds WHO limits only in carnivorous fish and mainly
in mining areas.
Objective 2:– No indications that modern amalgam processing is responsible
for the concentration of mercury measured in the aquatic
environment;
– Strong indications that jetting from land dredges in gold and
diamond operations are responsible for the flushing of pre-
modern mining mercury from the land overburden to the aquatic
environment.
