Transcript Mercury66 in Soils a..

Mercury in Soils and
Sediments:
Still River Basin and
Long Island Sound
Rachel Bronsther and Patrick Welsh
Mercury (Hg)
Hg comes in elemental and various organic
compounds and complexes (e.g. HgS, HgCl2, MeHg)
Exposure to organic Hg, in particular
methylmercury, has potential adverse effects in
humans. Exposure can be from ingestion or
inhalation. The nervous system is harmed by the
organic compound.
Elemental Hg can become methylated
by the environment.
Low Dose Effects
In children:
Neurotoxicity (e.g. problems with fine motor
skills, visual-spatial abilities, verbal memory)
In adults (long term, lose dose exposure):
weakness, tiredness, headaches, lack of
appetite, digestion problems, weight loss,
trembling of hands, numbness of extremities,
tingling of lips and tongue, etc.
Fish Consumption
EPA has determined that the primary
form of human exposure to
methylmercury is through
fish consumption.
Population at the greatest risk – children who eat or
whose mothers consume a large amount of fish
EPA has determined that a RfD of 0.1 ug MeHg/day
is acceptable.
Mercury in Soils
No decisive data seems to exist on what levels
in soil are “safe”.
In CT, up to 20 ppm of Hg in residential areas
is acceptable.
(Compared to MA, where legal residential levels are set at 10 ppm.)
No way to determine what percentage of Hg found in
soil is in its organic form without testing, as relative
abundances vary.
Mercury Levels
• Normal modern soil background levels for
mercury in the northeast are around 200 to
300 parts per billion
– Mostly due to atmospheric deposition
• Sediment samples from the Housatonic
River were higher than ‘normal’.
• Sources were traced to the Still River
– A north flowing tributary.
Still River
Flows through Danbury and Brookfield and into the
Housatonic River in New Milford.
It is 22 miles long and has a drainage area of 85
square miles.
Its mean flow of 377 ft3/sec.
Extreme levels
• Along the Still River levels of mercury in
sediment were found to be 5-10 ppm with
extremes up to100 ppm
– 500 times higher than background
• Where is the source?
Danbury, CT
Former hat-making capital of the world -20,000 hats/year were produced in 1800;
1 million hats/year by 1836. Mercury was
used in the felting process.
Located in the Still River Basin.
Mercury in Hat Making
• Mercury nitrate was used in the
felting process
• Workers in the Danbury factories
often suffered mercury poisoning
– Called “mad hatters”
– The origin of the phrase mad as a hatter
• The symptoms of the disease were
called the ‘Danbury shakes’
– symptoms of chronic mercury exposure
on the nervous system include increased
excitability, mental instability, tendency
to weep, fine tremors of the hands and
feet, and personality changes
Long Island Sound
LIS Cores
• Cores from the LIS were tested for mercury
in order to see the migration of mercury
from the Danbury source area
– North through Still River into Housatonic and
then emptied into LIS
• Results showed increased levels of mercury
– Levels were relatively low (400-800 ppb)
compared to that of the Still River
Sample Collection
• Surface Samples
• Cores
– Cores are generally sliced every 2cm up to 40 cm in
depth
– After 40 cm, the core is sliced every 5 cm
– The outsides of the core slices are cut off to prevent
cross contamination resulting from smearing the
outside
• Cubes are formed in this way
• Dried on Styrofoam plates
• Crushed and homogenized in plastic bottles
DMA (Direct Mercury Analyzer) 80
1.
Sediments are placed in open crucibles where they are weighed
(Crucibles are non-reactive heat-resistant nickel containers)
2.
3.
4.
5.
Pneumatic arm places the crucibles in the quartz combustion furnace
Sediments are dried at 300° C for 10 seconds
Thermally decomposed at 850° C for 180 seconds, which volatizes
Hg, water, carbon dioxide, and organic matter
Flowing oxygen carries this gas to a furnace where it is oxidized and
halogens, sulfides, and nitrogen oxides are trapped.
The remains go to an amalgamator in a third furnace.
1.
2.
3.
The amalgamator is made of gold particles that forms a metal alloy
with Hg.
Non-amalgamated products are carried out taking another 60 seconds
Amalgamator is heated intensely for 12 seconds and releases Hg vapor
to absorbance cells
DMA cont.
1.
2.
3.
Two cells (or cuvettes) are aligned with a small
collection flask between them where a mercury lamp
positioned at the end of the cells emits a single
wavelength that is absorbed by Hg0
Atomic absorption is measured by the
spectrophotometer, which is directly related to the
concentration
Surface area of the absorbance peak is transmitted to the
computer, which calculates the ppb Hg is a function of
the enter in weight
Calibration
A new calibration was required at the beginning of the
summer, as the machine had experienced some drift.
We calibrated, and recalibrated and recalibrated….finally, we
got Calibration “Gold”.
First we tried liquid standards, which did not work.
We ultimately calibrated using NIST and NRCC dry
standards.
Standards
We’ve been using 5 standards, 3 of which are
distributed by NIST and 2 from the NRC.
The standards include homogenized soil
ranging in Hg levels from 90 ppb to 3040
ppb.
Still River Basin GPS locations:
SR1 sample av ppb
SR1-176
1637.935
SR1-178
2405.095
SR1-180
2991.135
SR1-181
1817.59
SR1-182
2198.647
SR1-183
2017.157
SR1-185
1777.69
SR1-185
5888.093
SR1-186
1524.23
SR1-187
2136.52
SR1-188
1586.398
SR1-190
4173.405
SR1-190
7040.653
SR1-191
2929.038
SR1-193
7483.218
SR1-194
8104.16
SR1-195
1662.988
SR1-196
1652.15
SR1-197
1079.44
SR1-198
4995.47
SR1-199
2971.268
SR1-200
1568.358
SR1-201
1706.583
SR1-203
1812.993
SR1-204
5952.048
SR1-205
2795.603
SR1-206
6308.21
SR1-207
6789.597
SR1-209
1613.27
SR1-211
77122.32
SRs
SR2 sample avg ppb
13
3953.87
14
1967.645
15
4493.42
16
3267.565
17
857.195
18
3709.9
19
130517.9
20
4623.71
21
7433.69
22
3800.67
23
1936.07
24
2463.455
25
5516.61
26
4774.4
27
4796.04
28
5295.375
29
1970.415
30
2158.77
31
6990.005
32
12482.74
33
5449.63
34
6015.11
35
3615.645
36
54.35
37
8972.155
38
4518.47
SR, con’t.
Last Friday we took additional Still River samples (SR3), and
by the end of the summer we plan to have both SR2 and
SR3 values on the GPS map of the Basin.
WLIS75 C1 core
ppb vs. depth of WLIS 75C1 core
3500
3000
ppb Hg
2500
2000
1500
1000
500
0
0
20
40
60
80
100
depth (cm)
120
140
160
180
200
% H20 vs depth of WLIS75C1 core
0.9
0.8
% water
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
20
40
60
80
100
depth (cm)
120
140
160
180
200
dry density (g/cm^3)
calculated dry density vs. depth of WLIS75 C1
core
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
depth (cm)
120
140
160
180
200
Hg deposition vs. Depth of WLISC175
700
Hg deposition
600
500
400
300
200
100
0
0
20
40
60
80
100
depth (cm)
120
140
160
180
200
PW (Rachel and Pat) and PW (Bess) vs. depth of
WLIS75C1 core
80
Percent Water (%)
70
% water
(Rachel)
Bess % water
60
50
40
30
20
10
0
0
20
40
60
80
100
depth (cm)
120
140
160
180
200
Estimating Age of Sample
Age = 2001 – (depth (cm)/.44)
Because rough accumulation rate is 1cm = 2.2 years
And, the inverse of 2.2 is 1/.44
Around 1950-1970, some sort of dumping took place that
caused an unnatural increase of Hg (up to 3 ppm) in this
area of LIS. This was also a period of major floods….
Flood deposit???
?
depth (cm) Age of sample (yr)
1
1999
2.5
1995
3.5
1993
4.5
1991
5.5
1989
6.5
1986
7.5
1984
8.9
1981
9.5
1979
14.5
1968
19.5
1957
24.5
1945
29.5
1934
Conclusion:
The old hat factories of Danbury, CT serve as
a source of Hg. The source can be traced
down through the Still River (very high
concentrations; around 5-10 ppm) through
the Housatonic (still high) into the Western
LIS (400-800 ppb).