Survey of the Mercury Content of Earthworms on the South River Floodplain

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

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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.

DuPont

Has this changed appreciably?

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.

DuPont

Has this changed appreciably?

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

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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

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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)

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0.1

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-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

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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)



Mean Mercury (THg & MeHg) in Depurated Earthworms Living on the South River, VA, Floodplain

± 1 SEM

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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)



A Comparison of THg and MeHg Concentrations in Earthworms Living on the South River, VA, Floodplain

Wet Weight Basis (ww) ± 1 SEM

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To

tal

Mer

cury

(n

g/g

)

Wet Weight Basis (ww)

THg in Soil of the South River, VA, Floodplain



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0

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-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



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-5 0 5 10 15 20 25 30 35 40 45

Mea

n T

ota

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g (

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/g w

w)

Mean THg in Depurated Earthworms Living on the South River, VA, Floodplain




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Mea

n M

eth

yl M

ercu

ry (

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/g w

w)

Mean MeHg in Soil of the South River, VA, Floodplain




Outlier

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50

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-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




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Mean THg in Soil vs Concentration in Depurated Earthworms


R2 = 0.7193

0

500

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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)

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0 1 2 3 4 5 6 7

Soil MeHg (ng/g ww)

Ea

rth

wo

rm M

eH

g (

ng

/g w

w)


Mean MeHg in Soil vs Concentration in Depurated Earthworms

R2=.4201

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0

0.2

0.4

0.6

0.8

1

1.2

-5 0 5 10 15 20 25 30 35 40 45




BAF = [earthworm] / [soil]

Bioaccumulation Factor (BAF) for Total Mercury (THg) Using Depurated Earthworm Data

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0

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20

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-5 0 5 10 15 20 25 30 35 40 45




Bioaccumulation Factor (BAF) for Methyl Mercury (MeHg) Using Depurated Earthworm Data

BAF = [earthworm] / [soil]

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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)



A Comparison of THg and MeHg Concentrations in Earthworms Living on the South River, VA, Floodplain


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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

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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

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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.

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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:

Documents

Survey of the Mercury Content of Earthworms on the South River Floodplain