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Tracking Sources of Sewage in the Environmentby Stephen Mudge, Ph.D., and Ann Michelle Morrison, Sc.D.

Sewage is a complex and changeable mixture of natural and man-made components. No two sewage streams are exactly alike. Whether they originate from municipal sewage systems (e.g., discharges from combined sewer overflows [CSOs]), wastewater treatment plants (WWTPs), urban storm drains, agricultural runoff, or septic systems, there are unique chemical signatures within a sewage waste stream that can be used to track it. Release of sewage into the aquatic environment can result in exposing humans and ecological resources to fecal pathogens, pharmaceutical and personal care products (PPCPs), and domestic and industrial chemical waste (a simplified flow diagram for a sewage system is shown in Figure 1). As with any chemical forensic case, defining the problem is critical to identifying the correct forensic methods needed for finding the solution.

V o l u m e 9 • 2 0 1 0

Environmental Forensics

N O T E S

F o r m o r e i n f o r m a t i o n o n E x p o n e n t ’ s e n v i r o n m e n t a l s e r v i c e s , c o n t a c t :

Paul D. Boehm, Ph.D.Principal Scientist and Group Vice President, Environmental Group(978) 461-4601 pboehm@exponent.com

www.exponent.com

THE MATERIAL CONTAINED

IN THIS NEWSLETTER IS

INTENDED SOLELY FOR YOUR

INFORMATION; IT DOES

NOT CONSTITUTE LEGAL OR

TECHNICAL ADVICE, NOR

SHOULD IT BE RELIED UPON

AS SUCH.

Figure 1. General flow for a sewage system

Sewer

DWF

CSO

ScreeningPrimary Treatment

Clarifier

Disinfection (U.S.)Tertiary Treatment (International)

Grit forDisposal(landfill)

UV Irradiation

SurfaceWater Runoff

WastewaterRoadDrainage

Secondary TreatmentClarifier

Solids

Liquids Liquids

Digestion

Removal

BiologicalTreatment

Outfall of Treated Effluent into a River or Sea

ToWastewaterTreatmentPlant

Pumping Station

2 THE MATERIAL CONTAINED IN THIS NEWSLETTER IS INTENDED SOLELY FOR YOUR INFORMATION; IT DOES NOT CONSTITUTE LEGAL OR TECHNICAL

ADVICE, NOR SHOULD IT BE RELIED UPON AS SUCH.

When tracking sewage in the environment, the focus has been on detection of bacteria, typically fecal coliforms and Enterococcus. Most bathing water quality directives in the United States and Europe are couched in terms of these organisms. While some of these organisms may not be harmful in themselves, their presence can be indicative of other bacteria and viruses that are harmful. Counting bacteria is fraught with difficulty (Are they alive or dead? Are they related to humans or animals? Do they reproduce in the conditions of the test?). Where the source of fecal material is close to the sample collection point, it may be appropriate to conduct analyses of the different bacterial types through a range of molecular methods, which have been reviewed in a previous issue of EF Notes. Other chemical agents that may be useful in determining the source of the sewage include the following:

• Fecal Sterols and Stanols: In the human gut, cholesterol is converted to 5β-coprostanol, which is characteristic of most mammals. On the other hand, agricultural animals that graze on plants tend to produce more 24-ethyl coprostanol, so human inputs can be distinguished from those of herbivores by a simple ratio between these two compounds. The chemical structures of these two compounds are shown in Figure 2.

• Bile Acids: These compounds are related to the sterols above, but are appreciably more water soluble and will disperse rapidly rather than accumulate in suspended and settled sediments. Different animals produce different acids and a signature can be developed on the basis of the suite of chemicals present.

In the news:

On September 29, 2009, the Hampton Roads Sanitation District of Virginia Beach filed a settlement with the Justice Department, the U.S. EPA, and the Commonwealth of Virginia to pay a $900,000 civil penalty and take corrective actions to reduce alleged sewage releases into Chesapeake Bay that are estimated to cost at least $140 million. EPA’s enforcement and compliance strategy in Chesapeake Bay targets pollution sources that may substantially contribute to nitrogen, phosphorus, and sediment to impaired watersheds in the area.

The pollutants can arise from many sources, including sewer systems, WWTPs, urban stormwater runoff, septic systems, agricultural operations, and air deposition (ENS 2009). This type of focus necessitates methods that can distinguish between sources of these inputs.

Environmental News Service. 2009. Virginia Beach must control sewage overflows under costly settlement. http://www.ens-newswire.com/ens/sep2009/2009-09-30-091.asp.

• Fatty Acids: Seldom considered diagnostic, although methods to define the signature can allow discrimination among sources. For instance, it was possible to identify the type of restaurant contributing to the sediments in a harbour on the basis of the type of cooking oil used.

• Detergents: Many hundreds of potential chemicals are present in these formulations, but their chemical activity may make them difficult to trace or analyze. The compounds used in detergents also occur naturally, in many cases, and apportioning the correct source requires specialized techniques.

Figure 2. Digestion alters the chemical structure of common compounds. The distinguishing breakdown products that are released in feces can be used to identify the original source of the fecal pollution.

HO

HOH

Cholesterol(Cholest-5-en-3ß-ol)

5ß-Coprostanol(5ß–Cholestan-3ß-ol)

Gut bacteria

HO

HOH

ß-Sitosterol(24 Ethyl Cholest-5-en-3ß-ol)

24 Ethyl-coprostanol(24 Ethyl Cholestan-3ß-ol)

Gut bacteria

3 THE MATERIAL CONTAINED IN THIS NEWSLETTER IS INTENDED SOLELY FOR YOUR INFORMATION; IT DOES NOT CONSTITUTE LEGAL OR TECHNICAL

ADVICE, NOR SHOULD IT BE RELIED UPON AS SUCH.

• Fluorescent Whitening Agents: These compounds are added to laundry detergents to improve the whiteness of the washed clothes. They are also used by the paper industry and find their way through the WWTP into the effluent.

• Triclosan®: This is an anti-bacterial agent added to soaps, cosmetics, and toothpaste that also may survive passage through a WWTP and be found in the environment. This compound has an unusual behavior in waters as its solubility depends on the pH.

• Caffeine: This has been suggested as a tracking chemical for human sewage effluent. However, caffeine is water soluble (22 g/L) and will disperse rapidly to levels below the limit of detection for most analytical methods. Caffeine can be used as a tracer of the aqueous phase of wastewater, although care must be used in assigning sources when CSOs and untreated sources contribute to the system.

In addition to these chemical compounds, stable isotopes can certainly assist in source identification. The most common isotopes used for organic matter are 13C (carbon-13) and 2H (deuterium). The phrase “we are what we eat” is important here, as the stable isotopic signature of our food and metabolic processes, passed onto the chemicals we discharge, provides a way of determining source (Figure 3).

Depending on the case, one can develop a list of compounds that are NOT useful or diagnostic of source except in specialized cases. For instance, the influent to a WWTP may come from industrial sources that are authorized to discharge common metals such as copper, lead, and zinc. These metals are not useful in tracking the sewage per se. However, if the sources include speciality metals such as titanium or other less common metals, then metal analysis may be of use. Biochemical oxygen demand (BOD) may be indicative of organic matter addition, but on its own it does not show that sewage is involved. Naturally-occurring events may lead to reduction in the concentration of oxygen in a water body without the aid of sewage. Nutrients are frequently associated with sewage, and discharge may be responsible for eutrophic conditions (Figure 4).

Figure 4. A dense monoculture of green algae on the surface of a pond receiving sewage effluent

10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 21.0 22.0 23.0 24.0 25.0 26.0 27.0

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C20

C22

C15

C17

C12

C13

5β−Coprostanol

Cholesterol

24-Ethyl coprostanol

Sitosterol

rt (min)

δ13C = -25.1

δ13C = -28.4

δ13C = -32.1

δ13C = -31.6

Fatty Alcohols

Sterols andStanols

Figure 3. The 13C stable isotope values for the major sterols and stanols in the influent of a WWTP. The 5β coprostanol has a value distinctly different from those of the other major compounds, indicating its human origin, while the 24-ethyl coprostanol has a value similar to its parent compound derived from higher plants.

As with many environmental forensic cases, it is the weight of evidence derived from a range of markers or indicators that determines the sewage source. Tracking sewage can be accomplished if the correct suite of analytes is chosen. For example, to examine the extent of sewage dispersion, water soluble components might be the most appropriate to analyze for in the environmental samples. On the other hand, if one wants to examine the accumulation of sewage-related compounds in the environment, water insoluble compounds would be more suitable. In summary, the source of sewage can be tracked by analyzing for several components; one must understand the specific case details before determining the correct combination of analytes.

4 THE MATERIAL CONTAINED IN THIS NEWSLETTER IS INTENDED SOLELY FOR YOUR INFORMATION; IT DOES NOT CONSTITUTE LEGAL OR TECHNICAL

ADVICE, NOR SHOULD IT BE RELIED UPON AS SUCH.

Please contact Stephen Mudge or Ann Michelle Morrison at Exponent for further information about this issue of Environmental Forensics Notes; also, contact Gary Brugger for more information about WWTP operations in the United States.

About Exponent

Central to Exponent’s environmental expertise is a deep capability in environmental forensics. We have applied our expertise and experience to a wide variety of situations: refineries, former manufactured gas plants, mines, smelters, foundries, pulp and paper mills, wood treatment facilities, oil spills, fuel terminals, and many manufacturing facilities with contaminants in air, groundwater, surface water, sediment, and soil. We have more than 30 scientists and engineers with a variety of experience in environmental forensics. Points of contact for specific chemical classes are Walt Shields (metals and dioxins), Brian Murphy (TCE and other chlorinated solvents and MGP wastes), Paul Boehm (Petroleum), Paul Boehm and Tarek Saba (PAHs, PCBs, natural gas), Gary Bigham (mercury), Peter Mesard (perchlorate), and Stephen Mudge (isotope analysis).

Please contact Stephen Mudge, Ann Michelle Morrison, or Gary Brugger at Exponent if you would like additional information on this issue of our Environmental Forensics Notes.

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