Marine Chemistry in the Coastal Environment

27 Use of Silver and Zinc to Trace Sewage Sludge

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Dispersal in Coastal Waters F. R U T H E R F O R D and T. C H U R C H College of Marine Studies, University of Delaware, Newark, Del. 19711

Sewage sludge from the municipal plants of Philadelphia, Pennsylvania, and Camden, New Jersey, has been dumped some 12 miles off the mouth of the Delaware Bay from 1961 to 1972 in amounts averaging 389,340 m /year.(1) Since 1973 the disposal area has been moved some 40 miles off-shore. The City of Philadelphia commissioned the Franklin Institute Research Lab (FIRL) to investigate the dispersion of the sludge on the ocean bottom at the former dump site.(2) According to the FIRL findings, "The area has abundant life. . . well distributed number of species and that those present are healthy. Generally sediments appeared clean both in situ. . . and in samples brought to the surface". The only indication of potential pollution to Delaware shores that FIRL cited was that 52% of the seabed drifters recovered were found on Delaware's ocean beaches. Since the FIRL report depended on rather discriptive techniques of assessing sludge presence (3), a new method was deemed appropriate to trace the actual dispersion of the sludge material. 3

The secondary treated sludge is probably highly resistant to marine decomposition since i t has been activated already by anaerobic digestion at 35°C for 30 days. In its barged form it forms stable flocs, has a high moisture content (80%), moderate ignition content (38%), and his heavily laden with greases, oils, and tars, having a 17% bituminous extract.(4) Also, it appears to be concentrated in several trace metals.(5) In studying the New York Bight, silver was identified as a possible tag for tracing sludge materials.(6) Also, chromium, copper, lead, nickel, and zinc were enriched in contaminated sediments by factors of 10 to 100 over uncontaminated sediments in the New York Bight.(7) In the southern California coastal zone, the anthropogenic fluxes of several metals, including silver and zinc, silver and zinc fluxes have increased, with silver originating principally from direct municipal waste, and the zinc from either atmospheric washout and/or from outfall waste.(8) Comparison between barged sewage sludge from Philadelphia and 440

Church; Marine Chemistry in the Coastal Environment ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

27.

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Sewage Sludge Dispersal

441

normal bottom sediments from the v i c i n i t y of the dump site showed for 26 elements that s i l v e r and zinc had enrichment factors of 100 to 200 respectively.(5) Thus, i t seemed f r u i t f u l to employ assays of s i l v e r and zinc i n bottom sediments surrounding the Philadelphia dump s i t e to disclose the possible dispersion of sewage sludge. SAMPLING Sediment samples had been collected from the former nearshore dump site during cruises over the past four years. Figure 1 shows the date and location of each sample. Samples obtained from FIRL (7) were collected using a La Fond Dietz Grab, while Watling et.al. ( 72) and CMS 666-667 C73-'7b) used a O.lm^ Van Veen Grab. The sub-samples were taken from the i n terior portions of the grabs by use of plastic spatulas, transferred to plastic bags and frozen. The FIRL samples were obtained i n an already dry state. A l l precautions were taken to avoid contamination from dust and handling. f

ANALYSIS A. Reagents and Standards: A l l reagents used were purified i n a s i l i c a sub-boiler. Two commerical standards (Ventron, Inc. and Spex, Inc.), and one prepared i n the lab using pure s i l v e r nitrate were prepared to identical t i t e r and compared. A l l gave similar assay within 8%. The lab prepared s i l v e r nitrate standard was employed, stored i n 30% HNO3 i n a linear polythylene bottle, and the bottle completely covered by aluminum f o i l to prevent photoxidation of the solution. No standard materials were run because of absence of a matrix similar to sludge, or lack of both Zn and Ag assays. B. Sample Analysis: The samples were thawed and dried i n an oven at 80°C for 48 hours and then stored i n plastic M i l l i pore petri dishes. Normally, two duplicate 0.5 gram subsamples were weighed out from each mother sample, homogenized after drying, and each run with replicates. The sub-samples along with 3ml cone. HNO3 were placed i n teflon crucibles and capped with teflon l i d s . These capped crucibles were placed i n an aluminum bomb at about 80°C for 36-48 hours. After digestion the samples were transferred quantitatively into plastic centrifuge tubes and washed with d i s t i l l e d H 0. The samples were then centrifuged for 10 minutes, the supernate liquor decanted, and diluted to 10ml i n a glass volumetric flask for analysis. Silver was analyzed using a Varian Model 63 carbon rod flameless atomizer mated to a Varian Model 1200 atomic absorption spectrophotometer. The Model 1200, using an air-acetylene flame was employed i n the zinc analysis. The instruments settings used are l i s t e d i n Table I. 2


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CHEMISTRY

Table I Instrument settings for the Varian 1200 Atomic Absorption Unit and Model 63 Carbon Rod Atomizer used for the analysis of Ag and Zn i n digestates of Philadelphia sewage sludge diluted i n 0.1N HNOo.

Lamp

WaveLength (nm)

Slit (nm)

Lamp Current

Carbon Rod Settings

Ag

328.1

0.2

3mA

Zn

213.9

0.5

5mA

Dry

Ash

Atomize

1 at 20 5 at 10 6 at 2.5 sec. sec. sec. Flame Analysis

For each set of samples a standard curve was run, using values of 1 to 40 ppb for Ag and .5 to 5 ppm for Zn, which f i t in the linear working range of the spectrophotometer and i t s carbon rod atomizer. If any sample was out of this linear working range, i t was diluted and rerun. A blank was also de termined for each set of samples and the values were corrected when necessary. The hydrogen lamp was used to correct for nonatomic absorption, which was appreciable only for Zn at i t s shorter wavelength. Three separate 5μ1 inj ections from an Oxford pipette were placed i n the carbon rod for each sub sample, and the peak re t r i e v a l mode was used to obtain the absorbance of the s i l v e r . For zinc, two determinations of each sub-sample were aspirated into the air-acetylene flame and the absorbance determined using the three second integration mode.

RESULTS AND DISCUSSION Table II l i s t s the results of the anlaysis which are plot ted i n Figures 2, 3 and 4 respectively for s i l v e r , zinc and organic carbon concentration. The organic carbon was analyzed by a modified Coleman nitrogen analyzer coupled to a Beckman IR non-dispersive CO2 analyzer. The concentration recorded i s the average value for each sub-sample of the source material. The results indicate that s i l v e r and zinc are concentrated along shoals boardering the shipping channels entering Delaware Bay to the north and southwest of the dump s i t e . The rectangle of the dump site and the area due west seem to have the lowest concentration of s i l v e r and zinc. The only high reading i n the dump rectangle was recorded on the same day a sludge barge had discharged as "starred" i n Figures 2 and 3 and noted by "during dump". In Figure 2, "dumping ceased" notes a mininution


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Figure 1.

AND

CHURCH


443

Surface sediments used for trace metal survey to study dispersion of Philadelphia sewage sludge dumping ('61—72)

Figure 2.

Silver concentrations of sediments in vicinity of Philadelphia sewage sludge dump site (±5 ppm)



reddish-brown coarse sand, shell material

gray-brown fine s i l t

gray-black sand

gray-white sand, some shell material

7-14-72

7-14-72

7-14-72

7-14-72

7-20-72

7-20-72

7-20-72

7-20-72

7-20-72

M-5

M-6

M-7

M-8

M-9

M-10

M-ll

M-12

M-13

large brown sand particles

brown clay and large sand particles

brown coarse sand

gray-red brown sand

very coarse sand

brown and red sand

7-14-72

M-3

red-brown sand particles

7-14-72

Description

M-l

Station

Date of Collection

16.0, 6.3

14.0, 14.1

6.5

25.9, 20.9

18.5, 32.2

18.5, 15.6

54.4, 85.4

59.6, 6.0

30.9, 49.4

10.0

21.6, 35.5

[Ag], ppm

3.0, 3.1

12.2, 12.0

4.0

9.9, 6.0

10.3, 6.9

10.2, 19.5

52.3, 49.6

4.7, 7.0

4.1, 3.0

6.0

14.7, 14.6

[Zn], ppm

.38

.30

.11

.2

.11

.13

.39

.06

.16

.05

Organic Carbon (Wt%)

Bottom Sediments i n the Vicinity of Philadelphia Sewage Sludge Disposal (off Delaware) which are Analyzed for Silver and Zinc

Table II

155

293

5522

# of Nucula/ .lm* (9)


gray sand, s h e l l material

black fine s i l t

black fine s i l t with s h e l l material

very fine s i l t , dark gray, some shells

fine grain s i l t

gray, coarse sand, many s h e l l fragments

7-20-72

7-20-72

7-21-72

7-21-72

7-31-72

7-31-72

7-31-72

7-31-72

7-31-72

7-31-72

M-14

M-15

M-16

M-17

M-18

M-19

M-20

M-21

M-22

M-23

M-24

gray-brown medium sand

brown sand, s h e l l frag ments

brown sand

light gray to gray brown coarse sand

gray sand

7-20-72

Station

Description

Date of Collection PP

m

54.7, 18.4

44.1, 17.2

5.0, 10.1

73.0, 49.5

45.8, 47.7

23.8, 25.4

12.3, 13.7

9.1, 14.3

20.1, 19.6

38.3, 32.9

16.5, 29.6

A

[ g]i

Table II (cont'd.)

10.5, 15.3

6.7, 5.4

10.9, 8.1

11.1, 8.9

43.8, 45.7

6.4, 7.4

32.9, 38.1

30.1, 25.5

70.6, 68.7

10.0, 10.6

4.5, 4.6

[Zn], ppm

.14

.16

.28

.45

.36

.02

.43

.15

1.54

.16

.07


3575

3019

1010

2

of Nucula/ .lm (9)

8*

f

Si

I

C/3

π

3


very fine s i l t , dark gray

gray black s i l t

light colored sand, several s h e l l fragments

dark sand, some pebbles and s h e l l fragments

7-31-72

7-31-72

7-31-72

3-14-71

2-21-71

1-23-71

5-21-71

7-16-71

1-25-71

7-16-71

3-14-71

Station

M-25

M-26

M-27

E-2

E-4

E-5

E-9

E-13

E-7

E-ll

E-6

ppm

coarse sand, small shell fragments

medium grain sand

8.5, 10.4

6.8, 10.3

6.4, 8.9

27.7, 30.7

fine s i l t , few pebbles

5.8, 13.3

11.6, 6.2

10, 5.1

0.0, 0.0

49.5, 61.5

20.2, 6.3

0.0, 0.0

13.5, 10.3

31.2, 24.8

68.1, 43.9

49.3, 49.8

12.1, 17.9

6, 16.7

sand, pebbles, some shell fragments

ppm

73.9, 65.0

[Zn],

20.2, 23.9

60.4, 83.5

27.7, 49.8

126.7,36.8

[Ag],

coarse sand, large pebbles

brown sand, large pebbles

fine s i l t , gray-black

Date of Collection

Description

1

Table II(cont d.)

.1

.1

.1

.2

.1

.00

.4

.4

1.12

1.01

1.05


23

929

12238

.lm

2

(9)

# of Nucula/

s

m


Date of Collection

2-21-71

6-27-74

6-27-74

6-27-74

7-17-73

7-17-73

7-17-73

7-17-73

7-17-73

Station

E-l

CMS-4-3

CMS-4-4

CMS-4-2

CMS-3-3

CMS-3-7

CMS-3-2

CMS-3-6

CMS-3-4

medium to coarse sand, several large pebbles

fine gray sand, a few shell fragments

fine gray sand, many shell fragments

fine gray sand with pebbles & s h e l l fragments

medium sand, a few shell fragments

dark fine sand, many shells

fine sand, several shell fragments

medium sand, few shells and pebbles

fine sand, few pebbles, small s h e l l fragments

Description

10.0, 20,8

20.0, 21.6

8.0, 8.0

34.1, 30.4

5.7, 4.0

4.6

10.0, 5.8

6.3, 6.2

15.2, 20.0

[Ag], ppm

TableII (cont'd.)

5.0, 5.0

53.8, 49.1

27.0, 26.9

54.1, 54.6

4.8, 6.9

16.5

4.8, 10.6

5.3, 5.5

0.0, Ί.1

[Zn], ppm


7-17-73

1. 2.

medium to coarse sand, some shell fragments

Description

Philadelphia Sewage Sludge: 7-8-71 Alliquot Alliquot

CMS-3-5

Station

Date of Collection

7742, 9619 9961, 7619

3.9, 4.1

Table η (cont'd)

ppm

5997, 6871 6114, 6286

6.9, 7.2

[Znh

21.5 19.8

0.4


# of Nucula/ .lm* (9)

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RUTHERFORD

Figure 3.

Figure 4.

AND

CHURCH


449

Zinc concentrations of sediments in vicinity of Philadelphia sewage sludge dump site (± 5 ppm)

Percent organic carbon of sediments in vicinity of Philadelphia sewage dump site (±0.1%)


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i n metal concentration i n the years subsequent to dumping cessat i o n . These r e s u l t s suggest that when the sludge s e t t l e s to the bottom i t i s swept by the p r e v a i l i n g bottom d r i f t currents out of the dump s i t e p r i m a r i l y shoreward.(2) A l t e r n a t i v e l y , the strong p r e v a i l i n g thermocline, during the summer, may possi b l y be a s i g n i f i c a n t trap and d i s p e r s i n g agent. There i s l i t t l e agreement between the s i l v e r and z i n c r e s u l t s obtained by FIRL and t h i s r e p o r t , probably due to d i f f e r ent e x t r a c t i o n techniques and instrumentation. FIRL reported using only 5ml of concentration HCl per 100ml of sample. T h i s perhaps e x p l a i n s low metal recovery from an already r e s i s t a n t sludge that had r e c e i v e d secondary treatment. The v a r i a t i o n between sub-samples i n the areas o f high metal c o n c e n t r a t i o n i s s i m i l a r to that reported i n the New York Bight.(7) Such heterogeniety may i n d i c a t e poor mixing o f sludge and sediment. In another r e p o r t on the P h i l a d e l p h i a dump area d e a l i n g with benthos ( 9 ) , numerous Nucula proxima were d i s c o v e r e d a l s o i n the r e g i o n to the south and west o f the dump r e c t a n g l e . T h i s b i v a l v e species i s known to l i v e i n f i n e grained sediments with s u b s t a n t i a l organic content.(10) The number d e n s i t i e s o f Nucula (35,750 to 122,380/m ) are some of the h i g h e s t ever r e corded, suggesting that these deposit feeding b i v a l v e s may be e i t h e r feeding d i r e c t l y upon the sludge u t i l i z i n g i t s organic matter f o r sustenance, or i n d i r e c t l y u t i l i z i n g the carbon and n i t r o g e n of the a s s o c i a t e d microfauna. Both forms of behavior are suggested i n the caprophagic behavior of deposit feeders.(11) 2

Table I I I l i s t s the p a i r c o r r e l a t i o n c o e f f i c i e n t s between s i l v e r , z i n c , o r g a n i c carbon, and Nucula concentrations. There i s a confidence l e v e l f o r a r e l a t i o n s h i p greater than 98% f o r a l l but one of the p a i r s (Zn to Nucula). The c o r r e l a t i o n o f the numbers of Nucula proxima i n the area of high s i l v e r conc e n t r a t i o n support the i d e a that both t r a c e metals and p a r t i c u l a r i n f a u n a l organisms are s e n s i t i v e i n d i c a t o r s that can be used to d e l i n e a t e the d i s p e r s a l of sewage sludge. Implicated i n t h i s a s s o c i a t i o n i s a p o s s i b l e l i n k f o r the i n t r o d u c t i o n of sludge-derived t o x i n s and pathogens i n t o the marine food web, the evidence f o r which should r e c e i v e future a t t e n t i o n .

SUMMARY The t r a c e metals, s i l v e r and z i n c are h i g h l y concentrated i n the secondary t r e a t e d sewage sludge from the P h i l a d e l p h i a metropolitan area, and d i s p l a y s e n s i t i v e i n d i c a t i o n s as t r a c e r s f o r the bottom d i s p e r s a l of the sludge o f f the mouth of Delaware Bay. From such metal d i s t r i b u t i o n s , i t i s f a i r to conclude that the sludge has moved out of the former designated area of d i s p o s a l and d i s p e r s e d some tens of miles shoreward, toward the


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AND

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CHURCH

Table III S t a t i s t i c a l Correlation Between the Concentrations of Silver, Zinc, Organic Carbon, and Number Densities of the Mollusc Nucula proxima for Sediments i n the Vicinity of the Former Philadelphia Sewage Sludge Disposal Site.

Variable Pair

Correlation Coefficient(r)

(x,y)

Confidence of a Relation

(%)

.59

99% exists

.44

98% exists

Ag to # Nuc.

.52

98% exists

Zn to %C

.85

99.9%

.61

99% exists

.37

90% exists

Ag to Zn Ag to %C

Zn to #

(org)

(org) Nuc.

%C (org) to #

where

Nuc.

Zxy - (ZxZy/n)

|_( for

exists

Σχ

n

)

Marine Chemistry in the Coastal Environment

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