Direct evidence of histopathological impacts of wastewater discharge on resident Antarctic fish (Trematomus bernacchii) at Davis Station, East Antarctica

Highlights

• Histological alteration in Antarctic cod exposed to wastewater from Davis Station.

• Severity of gill and liver pathologies directly related to proximity to outfall.

• Prevalence and severity of alteration decreased with distance from the outfall.

• Higher level of treatment required to minimise impacts to marine environment.

Abstract

During the 2009/2010 summer, a comprehensive environmental impact assessment (EIA) of the wastewater discharge at Davis Station, East Antarctica was completed. As part of this, histological alteration of gill and liver tissue in Antarctic Rock-cod (Trematomus bernacchii) from four sites along a spatial gradient from the wastewater outfall were assessed. All fish within 800 m of the outfall exhibited significant histological changes in both tissues. Common pathologies observed in fish closest to the outfall include proliferation of epithelial cells with associated secondary lamellar fusion in the gills and multifocal granulomata with inflammation and necrosis as well as cysts in the liver. Fish from sites >800 m from the outfall also exhibited alterations but to a lesser degree, with prevalence and severity decreasing with increasing distance from the outfall. This study highlights the value of histopathological investigations as part of EIAs and provides the first evidence of sub-lethal alteration associated with wastewater discharge in East Antarctica.

Introduction

Antarctic coastal waters are generally considered pristine. However, they can be interspersed with localised regions of high level pollution associated with human activity (Evans et al., 2000, Snape et al., 2001a). Concurrent with the increase of human presence, coastal contamination has become a significant concern in Antarctica (Clarke and Harris, 2003, Poland et al., 2003). There are three main sources of anthropogenic contamination in the Antarctic marine environment: 1. Abandoned waste refuse sites (Sheppard et al., 2000, Snape et al., 2001b, Stark et al., 2006); 2. Accidental fuel spills (Kennicutt Ii et al., 1991, Snape et al., 2006); and 3. Wastewater discharges (Green and Nichols, 1995, Gröndahl et al., 2009, Howington et al., 1992).

Wastewater treatment in Antarctica is a relatively recent development. Prior to the enforcement of the Protocol on Environmental Protection to the Antarctic Treaty in 1998, wastewater was either incinerated in open air or discharged directly into the sea without any level of treatment (Bargagli, 2008, Tin et al., 2009). Of the 41 permanent Antarctic stations (COMNAP, 2014), only 63% have some form of treatment facilities (Gröndahl et al., 2009). Stations with treatment facilities are often affected by a range of conditions which inhibit their operational efficiency including; fluctuating human populations, limited water availability, inappropriate design, lack of maintenance, the isolation of stations and associated difficulties in supplying equipment, as well limitations on size of buildings (Stark et al., Unpublished-a). Environmental contamination from wastewater depends on the volume and composition of wastewater released, the level of treatment it receives prior to discharge, and on the biological and physical environment that the wastewater is released into (Tin et al., 2009).

Wastewater in Antarctica is a complex mix of contaminants, containing not only human waste but also grey water from kitchens, showers, and wastewaters from other buildings which may include detergents, cosmetics, medications, chemicals being used on station, as well as wastewaters from workshops and scientific laboratories (Smith and Riddle, 2009, Stark et al., Unpublished-a). Such a complex mixture entering the marine environment would be likely to have an effect at some level. In addition, traditional wastewater treatment technologies are designed to primarily reduce microbiological loads and the concentration of nutrients. They are not designed to remove contaminants such as dissolved metals or persistent organic pollutants, which require advanced treatment technologies to ameliorate. Such high levels of treatment are significantly more expensive, difficult to install and maintain, and are absent from Antarctica.

Prior to 1991, wastewater disposal at Davis Station was by combustion until a secondary wastewater treatment facility was commissioned (Green and Nichols, 1995). This treatment facility was however, ineffective over the summer months when the station population increased markedly, leading to decommission and infrastructure removal in 2005 (Pyper, 2009). Since 2005, wastewater has undergone simple maceration and direct discharge to the sea at the shore line (Smith and Riddle, 2009). Under the Protocol on Environmental Protection to the Antarctic Treaty, also known as the Madrid Protocol (1991), of which Australia is a signatory, wastewater and domestic liquid may be discharged directly into the sea, provided conditions exist for initial dilution and rapid dispersal. In addition, wastewater from stations with populations of 30 or more must be treated by at least maceration (Annex III, article 5).

In the summer season of 2009/2010, a comprehensive Environmental Impact Assessment (EIA) of the Davis Station wastewater outfall investigated the properties of the wastewater including its potential toxicity to local species, the dispersal and dilution characteristics of the receiving environment, and nature and extent of impacts on benthic communities and on key biota in the receiving coastal environment (Stark et al., Unpublished-a, Leeming et al., 2014, Stark et al., 2011). This program represented the first comprehensive evaluation of physical, chemical, biological and ecotoxicological properties of wastewater effluent in Antarctica, using a multiple lines of evidence approach to the environmental impact assessment of open coastal wastewater disposal in Antarctica. Ecological risk assessment (ERA) is a tool commonly used within EIAs to determine likely or actual adverse effect of pollutants on ecosystems and their components (Depledge and Fossi, 1994). Applicable biological ERA measures to determine potential impact extend across the biological hierarchy from the subcellular level, through to the community level. Cells and tissues represent a mid-point in this hierarchy, where a change or ‘irregular alteration’ in structure signals a potential biomarker (Hinton et al., 1992, Hinton et al., 2001, Schlenk et al., 2008). Histological biomarkers represent ideal risk assessment tools as change in cellular composition and/or structure; indicate the net result of adverse biochemical and physiological change within the cell. Direct observation of cellular alteration enables identification of sub-lethal effects in situ, potentially acting as early warning signals of long term effects due to pollutant toxicity (Hinton and Lauren, 1990). Given that the composition and chemical behaviour of effluents in situ is often unknown, histology has long been recognised as a sensitive biomarker able to detect biological effects of wastewater exposure before specific chemical analyses are conducted (Nowak, 1996).

Detrimental effects of wastewater effluent exposure on higher level marine biota are well known in other regions of the world, yet have not been adequately quantified in Antarctica. The paucity of research directed towards assessing and understanding impacts on keystone species, such as the common Antarctic Emerald Rock-cod (Trematomus bernacchii), highlights a significant gap in ecological risk assessment specific to the Antarctic region. To mitigate this gap in knowledge, T. bernacchii was included in the Davis Station EIA program as a bioindicator species for in situ contaminant impact.

A number of studies have shown T. bernacchii to be a good biomarker species (Miller et al., 1998, Jiménez et al., 1999, Di Bello et al., 2007). Rock cod are common benthic teleosts in Antarctic coastal waters (La Mesa et al., 1996, Romano et al., 1997). The species are long lived with females growing faster and living longer than males (approximately 21 years for females and 16 years for males; La Mesa et al., 1996). T. bernacchii are advantageous feeders which seek out sedentary prey or lye and wait to ambush mobile prey species (Keist, 1993). Prey species vary from region to region and depends on species availability (Kiest, 1993, Vacchi et al., 2000). T. bernacchii are potentially exposed to contaminants by bioaccumulation of contaminants via direct sediment contact and their diet. Rock-cod have a narrow home range, residing within an approximate 500 m radius, and therefore are likely to reflect the impact of localised contamination in the environment at or near the site of collection (Evans et al., 2000, Herbert et al., 2003, Kawaguchi et al., 1989).

T. bernacchii bioaccumulate specific metals at higher concentrations relative to other common Antarctic fish species, increasing their likely susceptibility to environmental contamination (Albergoni et al., 2000, Santovito et al., 2000). To date, ecotoxicological research on T. bernacchii has focused on Ethoxyresorufin-O-deethylase (EROD) enzyme and CYP1A induction as a surrogate measure of polyaromatic hydrocarbons (PAH) and polychlorinated biphenyl (PCB) exposure (Miller et al., 1998, Benedetti et al., 2007, Di Bello et al., 2007, Benedetti et al., 2009, Lurman et al., 2010;). Only one previous study has applied histology as a potential indicator of contamination impact using T. bernacchii. Evans et al. (2000) found significant pathologies in fish within close proximity to McMurdo Station (Evans et al., 2000). Pathologies included periductal inflammation and necrosis in the liver and epithelial hyperplasia, lamellar fusion and aneurysm of the gills. Abnormalities were more prevalent in fish from Winter Quarters Bay (a known contaminated bay) as compared to Back Door Bay (a reference site, free from obvious signs of human impact). However a significantly higher hepatic somatic index and fish condition factor were observed in fish from Winter Quarters Bay, which would usually indicate better health. The aetiology of pathologies observed was unknown. However, metal concentrations in fish tissue did not differ between sites, leading the authors to rule out metal contamination, and suggest organic pollutants or pathogens introduced via the McMurdo Station wastewater outlet as probable causes.

To evaluate histology as a biomarker of contamination impact from the wastewater outfall at Davis Station, liver and gill tissue of T. bernacchii were examined for histopathological alteration. Prevalence and severity of pathologies were compared between four sites along a spatial gradient from the point of discharge to 9 km south of the wastewater outfall.