Environ. Sci. Technol. 2007, 41, 792-802
Detection of Intermittent Sewage Pollution in a Subtropical, Oligotrophic, Semi-enclosed Embayment System Using Sterol Signatures in Sediments CATHERINE PRATT,* JAN WARNKEN, RHYS LEEMING, JAMES M. ARTHUR, AND DARREN I. GRICE Centre for Aquatic Processes and Pollution, School of Environmental and Applied Sciences, Griffith University, Gold Coast Campus, PMB 50 Gold Coast Mail Centre, QLD 9726 Australia
A field study was conducted to investigate sewage inputs at popular anchorages in Moreton Bay, a sub-tropical, semienclosed embayment system in Southeast Queensland, Australia. Sterol biomarkers were quantified in sediments revealing low levels over a spatial and temporal scale consistent with a shallow, oligotrophic, highly dynamic, sand dominated system. Despite low concentrations (ng/g) and high variability, relevant sterol/stanol pairs remained wellcorrelated and were successful in identifying an unexpected once-off pollution event from a point source at Moreton Bay Island. During this incident, the main human sewage biomarker, coprostanol, was found at a concentration of 1.4 µg/g, with a coprostanol/5R-cholestanol ratio of 3.2. Other than this one incident, sterol levels were consistently low even when anchorages were at full capacity. Thus, sewage from recreational vessels was found to have very little effect on sediment quality at anchorages in Moreton Bay and Gold Coast Broadwater.
Introduction Most government authorities around the world now accept that issues surrounding the deterioration of water quality in coastal regions will become a major challenge over the next 50 years (1-3). This is largely attributed to intense economic development in these much sought after areas (4). In Australia, legislation regarding the release of sewage into coastal waters has recently been reviewed and enacted to include new provisions relating to developing more streamlined criteria for sewage discharges, much like U.S. guidelines (2). These new provisions include the discharge of sewage from recreational vessels (3). Recent research regarding sewage inputs in the coastal region of southeast Queensland (5, 6) identified a large number of possible sources that could contribute to the deterioration of these waterways. One of these possible sources that has been largely overlooked is the large increase in recreational vessels over the past 20 years. As in the case of marinas, anchor sites are locations where boats tend to aggregate and people use on-board facilities, * Corresponding author phone +61 (0) 7 4753 4224; fax +61 (0) 7 4772 5852; e-mail
[email protected]. 792
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 41, NO. 3, 2007
which, if not connected to holding tanks, result in a source for sewage input. Marinas and anchor sites are very similar in that they are usually located in calm, protected waters where tidal flushing is low. Marinas are well-known to act as a sink for pollutants (7-9). However, there is one major difference between marinas and anchor sites. Popular anchor sites are also used for human recreational activities such as swimming, diving, jet skiing, etc. In this respect, sewage pollution from recreational vessels at anchor sites could present a greater risk to human health along with adverse affects on the health of the ecological community. Sewage contamination has traditionally been determined by enumeration of microbiological indicators, such as faecal coliforms. Many researchers have questioned the reliability of these methods mainly due to their non-specificity (10, 11) and unknown regrowth/die-back rates, especially in marine waters (12, 13). An additional method of detecting sewage pollution by researchers worldwide is by the use of sterol biomarkers. Sterol biomarker fingerprinting in both the water column and the sediments from marine and freshwater environments has been used with considerable success to trace sewage plumes and to identify the likely origin of sewage pollution (14, 15). Compounds such as coprostanol (5β-cholestan-3β-ol) can be used in conjunction with other sterols to indicate the relative abundance of sewage in sediments. Additionally, many researchers utilize sterol biomarker ratios, rather than relying solely on absolute concentrations for providing pollution threshold levels (16, 17). Ten sterol biomarkers were used in this study. Systematic, trivial names, and source identification are given in Table 1. This research served to illustrate the use of faecal sterols as additional indicators in the determination of non-point source sewage inputs at popular anchor sites in southeast QLD Australia.
Experimental Procedures Sample Design, Collection, and Preparation. Five anchor and three reference sites were chosen for investigation within Moreton Bay and Gold Coast Broadwater, QLD (Figure 1), for 1 year from December 2001 to December 2002. All eight sites were sampled repeatedly throughout the year. The Moreton Bay and Broadwater system on the east coast of Australia is a sub-tropical, shallow embayment close to two major urban centers of around 2 million people (i.e., the cities of Brisbane and the Gold Coast, with ∼75 000 registered recreational vessels (18). During each visit, sediment samples were taken by SCUBA. Physiochemical measurements and weather data were also collected for each site visit. Anchor sites at Moreton Bay and the Gold Coast Broadwater were chosen to represent the diversity of site characteristics and influences to this highly dynamic system. Site characteristics taken into consideration included: estuarine/ marine influence, proximity to land (urban and remote), vegetative surroundings (algal substrates or proximity to higher plants such as mangroves), and human/herbivore inputs. It must be emphasized that the reference station Wave-Break Island (Figure 1) was chosen to represent the Marine Stadium anchor site due to the fact that both sites would most likely receive the same land, urban and natural source influences; however, Wave-Break Island is not frequented by boats. Additionally, a rock wall and a fast flowing channel of water separate the two sites. Possible sources and characteristics of each sample site are given in Table 2. 10.1021/es061450f CCC: $37.00
2007 American Chemical Society Published on Web 12/15/2006
TABLE 1. Systematic (IUPAC) and Trivial Names and Description of Sterols for Source Identification systematic name (IUPAC)
trivial name
description C27 sterols
5β-cholestan-3β-ol
coprostanol
human faecal biomarker; high relative amounts indicate fresh human faecal contamination present in sewage sludges major ubiquitous sterol; C27 precursor to 5R- and 5β-stanols normal reduction product of cholesterol; thermodynamically most stable isomer is ubiquitous
5β-cholestan-3R-ol cholest-5-en-3β-ol
epi-coprostanol cholesterol
5R-cholestan-3β-ol
cholestanol
24-ethyl-5β-cholestan-3β-ol 24-ethyl-5β-cholestan-3R-ol 24-ethylcholest-5-en-3β-ol
C29 sterols 24-ethylcoprostanol 24-ethyl-epi-coprostanol 24-ethylcholesterol (sitosterol)
herbivore faecal biomarker also present in some herbivore faeces C29 precursor to 5R- and 5β-stanols; usually used as a terrestrial sterol biomarker 24-ethyl-5R-cholestan-3β-ol 24-ethylcholestanol (sitostanol) thermodynamically most stable isomer is ubiquitous 24-ethylcholestan-5,22E-dien-3β-ol stigmasterol usually used as a terrestrial sterol biomarker 24-ethyl-5R-cholestan-22E-en-3β-ol stigmastanol algal sterol biomarker, also found in reducing environments
sterol ratios (trivial names given)
threshold level
coprostanol/5R-cholestanol
>0.3
coprostanol/cholesterol
0.2
epi-coprostanol/coprostanol 24-ethylcoprostanol/sitostanol
variable >0.3
24-ethylcoprostanol/sitosterol
0.2
description main human sewage ratio; if the ratio of coprostanol/cholestanol is 100 ha
>100 ha coastal woodland
yes
sand and mollusk debris fine silt
close by
high (drains)
none
none
revegetated for sand stabilization
none
coarse sand
none
none
micro + macro
none
none
none
sand
occasionally used by 1-5 recreational fishermen
none
none
micro
abundant, >100 ha
(coastal woodlands upstream)
yes
sand
occasionally boat anchored in nearby channel
close by
none
none
none
revegetated for sand stabilization
none
coarse sand
protected in SE winds, 0-10 boats weekdays,
