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Survey of the Mercury Content of Earthworms on the South River Floodplain. John Cianchetti and Dean Cocking, James Madison University, Harrisonburg, VA Bill Berti, DuPont Co., Central Research and Development, Newark, DE South River Science Team April 8, 2008. Objectives of Study. - PowerPoint PPT Presentation
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Survey of the Mercury Content of Survey of the Mercury Content of Earthworms on the South River Earthworms on the South River
FloodplainFloodplain
John Cianchetti and Dean Cocking, James Madison University, Harrisonburg, VA
Bill Berti, DuPont Co., Central Research and Development, Newark, DE
South River Science Team April 8, 2008
2
Objectives of Study
Conduct a survey of Hg concentrations in earthworms to understand the extent to which mercury bioaccumulates in earthworms.
Evaluate the relationship between total mercury (THg) and methyl mercury (MeHg) concentrations in earthworm and paired soil samples.
3
Floodplain Earthworm Sample Locations
Grand Caverns
Abbee Road Bridge
Confluence
Ridgeview Pk
North Pk
Crimora
Hopeman Pkwy
Robert Turk Rd
Belvidere Rd
Forestry Ctr
Dooms
Basic Pk
CNF
GGC
BVD
FOR
CRM
RTR
DMS
HPK
BPK
NPK
ARB
RVPPoint sourcePoint source
Waynesboro
Staunton
Control site
4
Sample collection procedure
A 10x10 square meter grid was established in each location and was subdivided into 1x1m quadrats
5 of the quadrats were randomly selected for sampling.
5
Sample collection procedure
Excavated a surface layer of 50 cm at each quadrat to collect minimum of 30 individual earthworms.
Soil samples were collected from this surface layer at each quadrat.
The aliquots from each quadrat were homogenized within a plastic bag and placed in vials for total and methyl mercury analysis; five composite samples per location corresponding to each earthworm sample.
Residual soil from each quadrat was combined to create a composite sample at each location sample used for soil property characterization.
6
Sample Processing: Earthworms
The earthworms were transported to the laboratory in a cooler.
Earthworm samples were sequentially rinsed with DI water in a series of six pyrex glass dishes.
A sub sample of at least 12 earthworms from three quadrats from each location were processed as undepurated samples which were frozen immediately.
A similar sized sample from each quadrat was depurated for 24 hours in a container with moist filter paper, and then frozen.
All samples were shipped to Studio Geochemica for analysis
7
Summary Earthworm and Soil Sampling Design at Each Location
Quadrat No. Earthworms Soil
Total Hg MeHg
Un-
deparated† De-
parated Un-
deparated† De-
parated† Total Hg MeHg† XAS‡
Soil test§
1 1 1 1 1 1 1 0.2 2 1 1 0.2 3 1 1 1 1 1 1 1 0.2 4 1 1 0.2 5 1 1 1 1 1 1 0.2
Total samples/location 3 5 3 3 5 3 1 1
† Specific quadrat samples for analysis will be randomly selected. ‡ X-ray Absorption Spectroscopy § A composite sample with soil from the quadrats.
All Samples were shipped to Studio Geochemica for analysis
8
Detection Limits
With the exception of methyl mercury in earthworms at the control site, analyzed samples all had values well above minimum detection limit (MDL) and the practical quantitative limit (PQL) for the fresh weight samples. (Provided by Studio Geochemica)
9
0.1
1
10
100
1000
10000
100000
-10 0 10 20 30 40 50
Me
rcu
ry (
ng
/g)
Thg (Wet Weight Basis)THg (Dry Weight Basis)MeHg (Wet Weight Basis)MeHg (Dry Weight Basis)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Downstream River Kilometer (0 = Waynesboro Point Source)
Mean Total Mercury (THg) and Methyl Mercury (MeHg) in Soil of the South River, VA, Floodplain
± 1 SEM
10
1
10
100
1000
10000
100000
-10 0 10 20 30 40 50
Mer
cury
(n
g/g
)Thg (Wet Weight Basis)Thg (Dry Weight Basis)Mehg (Wet Weight Basis)Mehg (Dry Weight Basis)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Downstream River Kilometer (0 = Waynesboro Point Source)
Mean Mercury (THg & MeHg) in Depurated Earthworms Living on the South River, VA, Floodplain
± 1 SEM
11
1
10
100
1000
10000
-10 0 10 20 30 40 50
Me
rcu
ry (
ng
/g w
w)
THg (Depurated Earthworms)THg (Undepurated Earthworms)MeHg (Depurated Earthworms) MeHg (Undepurated Earthworms)
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
A Comparison of THg and MeHg Concentrations in Earthworms Living on the South River, VA, Floodplain
Wet Weight Basis (ww) ± 1 SEM
12
0
5000
10000
15000
20000
25000
30000
-5 0 5 10 15 20 25 30 35 40 45
To
tal
Mer
cury
(n
g/g
)
Wet Weight Basis (ww)
THg in Soil of the South River, VA, Floodplain
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Downstream River Kilometer (0 = Waynesboro Point Source)
13
0
5000
10000
15000
20000
25000
-5 0 5 10 15 20 25 30 35 40 45
Mea
n T
ota
l M
ercu
ry (
ng
/g w
w) Wet Weight Basis (ww) ±
1 SEM
Mean THg in Soil of the South River, VA, Floodplain
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
14
0
500
1000
1500
2000
2500
3000
3500
4000
-5 0 5 10 15 20 25 30 35 40 45
Mea
n T
ota
l H
g (
ng
/g w
w)
Mean THg in Depurated Earthworms Living on the South River, VA, Floodplain
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Wet Weight Basis (ww) ± 1 SEM
15
0
2
4
6
8
10
12
14
-5 0 5 10 15 20 25 30 35 40 45
Mea
n M
eth
yl M
ercu
ry (
ng
/g w
w)
Mean MeHg in Soil of the South River, VA, Floodplain
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Wet Weight Basis (ww) ± 1 SEM
Outlier
16
0
50
100
150
200
250
-5 0 5 10 15 20 25 30 35 40 45
Mea
n M
eth
yl H
g (
ng
/g w
w)
Mean MeHg in Depurated Earthworms Living on the South River, VA, Floodplain
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Wet Weight Basis (ww) ± 1 SEM
17
Mean THg in Soil vs Concentration in Depurated Earthworms
Wet Weight Basis (ww)
R2 = 0.7193
0
500
1000
1500
2000
2500
3000
3500
0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000
Soil THg (ng/g ww)
Ear
thw
orm
TH
g (
ng
/g w
w)
18
0
20
40
60
80
100
120
140
160
180
200
0 1 2 3 4 5 6 7
Soil MeHg (ng/g ww)
Ea
rth
wo
rm M
eH
g (
ng
/g w
w)
Wet Weight Basis (ww)
Mean MeHg in Soil vs Concentration in Depurated Earthworms
R2=.4201
19
0
0.2
0.4
0.6
0.8
1
1.2
-5 0 5 10 15 20 25 30 35 40 45
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Wet Weight Basis (ww)
BAF = [earthworm] / [soil]
Bioaccumulation Factor (BAF) for Total Mercury (THg) Using Depurated Earthworm Data
20
0
10
20
30
40
50
60
70
80
-5 0 5 10 15 20 25 30 35 40 45
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
Wet Weight Basis (ww)
Bioaccumulation Factor (BAF) for Methyl Mercury (MeHg) Using Depurated Earthworm Data
BAF = [earthworm] / [soil]
21
1
10
100
1000
10000
-10 0 10 20 30 40 50
Mer
cury
(n
g/g
)
Thg (Wet Weight Basis)
Mehg (Wet Weight Basis)
Downstream River Kilometer (0 = Waynesboro Point Source)
RVP ARB NPK BPK HPK DMS RTR CRM FOR BVD GGC CNF
A Comparison of THg and MeHg Concentrations in Earthworms Living on the South River, VA, Floodplain
Wet Weight Basis (ww)
22
Cation Exchange Capacity by Location
0
2
4
6
8
10
12
14
16
RVPARB
NPKBPK
HPKDM
SRTR
CRMFO
RBVD
GGCCNF
Location
Ca
tio
n E
xc
ha
ng
e C
ap
ac
ity
(m
eq
/10
0g
)
Soil Ph By Location
0
1
2
3
4
5
6
7
8
Location
Ph
Percent of Soil Organic Matter by Location
0
1
2
3
4
5
6
RVPARB
NPKBPK
HPKDM
SRTR
CRMFOR
BVDGG
CCNF
Location
Pe
rce
nt
Org
an
ic M
att
er
Percentage of Soil composed of Sand by Location
0
10
20
30
40
50
60
70
80
90
Location
Pe
rce
nt
Sa
nd
Pa
rtic
les
Soil Characteristics
23
How much Hg is tied up in earthworms on the floodplain?
5-yr floodplain - 2094 acres = 8.5 E+6 sq m Mean earthworm fresh wt = 20.6 g / sq m
Estimated earthworm fresh wt 5-yr floodplain= 1.7 E+8 g
Mean THg in undepurated earthworms = 2447 ng/g Mean MeHg in undepurated earthworms = 66 ng/g
Total Hg in earthworms on 5-yr floodplain = 4.3 E+17 ng = 426 grams Total MeHg in earthworms on 5-yr floodplain = 1.2 E+16 ng = 11.6 grams
For the large amount of area involved, this appears to be a very small proportion of the Hg present on the floodplain.
SOURCES OF ERROR IN THIS ESTIMATE: Not all of the floodplain is suitable earthworm habitat (eg parking lots); un-weighted mean biomass and THg/MeHg may be over or under estimates of true values
24
Summary
Both forms of mercury are present in the soil and earthworms of the floodplain at an elevated level.
The pattern of total mercury distribution is superficially similar to that previously observed in other organisms in the river.
The methyl mercury concentrations do not follow a discernable pattern.
Total mercury concentrations in earthworm tissues are proportional to the total mercury concentration of the soil, however this is not the case in the methyl mercury concentrations.
25
Path Forward
What is the food chain position of earthworms within these ecosystems?
What is the relationship between these results and those from studying other organisms along the South River?
How do these results compare with studies of the uptake of Hg by earthworms from other terrestrial sites including sewage sludge deposits and industrial wastes.
It is of interest to pursue what causes the fluctuations in MeHg within the earthworm tissues in relation to soil MeHg content. While soil is likely a contributing factor, other variables may also play a role:
microhabitat time of sampling, earthworm species composition (affects feeding habits) endogenous vs exogenous origin of MeHg etc.
While it appears that the observed patterns of Hg content in earthworms are not unexpected, there are some questions of passing interest: