Using Fish Biomarkers to Monitor Improvements in Environmental Quality

—The percentage of splenic tissue occupied by macrophage aggregates and hepatosomatic index (HSI) were evaluated in rock bass Ambloplites rupestris from Burlington Harbor, Vermont. In 1992, fish collected from the inner Burlington Harbor area had a significantly greater percentage of splenic tissue occupied by macrophage aggregates and greater HSI than did fish from reference sites. These biomarkers often are correlated with exposure to various contaminants (e.g., polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and some heavy metals, which were found in Burlington Harbor sediments during surveys in 1990 and 1991). Contaminants are believed to have entered Burlington Harbor through the city’s main sewage treatment plant, which discharged effluent into the harbor for many years. In 1994, the city completed a significant upgrade of this treatment plant, which included an extension of the effluent pipe beyond the inner harbor area. In 1999, rock bass were again collected from Burlington Harbor as an index of whether there was any improvement in environmental quality. Our data showed a significantly lower percentage of splenic tissue occupied by macrophage aggregates and significantly lower HSI among nine age4 rock bass in 1999 than among six age-4 rock bass in 1992. The significant changes in these biomarkers suggest decreased exposure to contaminants. Our study reinforces the value of macrophage aggregates and HSI as biomarkers of environmental contamination, and the correlation with remedial action shows their potential utility in documenting improvements in environmental conditions. Biomarkers are measures of cellular, biochemical, molecular, or physiological change in an organism that indicate exposure to or the effects of environmental contaminants. Despite the fact that a large number of biomarkers have been developed and used to monitor environmental health since * Corresponding author: [email protected] Received November 5, 2004; accepted April 3, 2005 Published online August 12, 2005 the mid 1980s, there is still no consensus on the best suite of markers or on their sensitivity and reliability (Lam and Gray 2003). Macrophage aggregates, or melanomacrophage centers, are structures in the spleen, kidney, and sometimes liver of fishes that have been used as nonspecific cellular biomarkers of physiological stress due to exposure to environmental contaminants. Since the mid 1980s there has been a growing body of evidence supporting the utility of macrophage aggregates as biomarkers. Numerous studies have shown increased macrophage aggregate metrics (number, size or percentage of tissue occupied) in fishes from contaminated areas when compared with conspecifics from less contaminated reference sites (Wolke et al. 1985; Blazer et al. 1987; Macchi et al. 1992; Blazer et al. 1994; Couillard and Hodson 1996; Lindesjoo et al. 1996; Facey et al. 1999; Fournie et al. 2001). Macrophage aggregate metrics are used in a number of monitoring programs, including the U.S. Environmental Protection Agency’s Environmental Monitoring and Assessment Program (EMAP) and the U.S. Geological Survey’s Biomonitoring of Environmental Status and Trends (BEST) Program (Summers et al. 1997; Schmitt and Dethloff 2000). Organ-level biomarkers, particularly the hepatosomatic index (HSI), also have been used as biomarkers of contaminant exposure (Goede and Barton 1990). Because the liver is so important in detoxification, exposure to contaminants can lead to an increase in liver size from hypertrophy (an increase in size), hyperplasia (an increase in number) of hepatocytes (Goede and Barton 1990; Hinton and Lauren 1990), or both. Studies evaluating the relative liver size of fishes from contaminated and reference sites often utilize the HSI, which expresses liver size as a percentage of total body weight (Facey et al. 1999).