The Aquatic Oligochaete Tubifex tubifex as a Water Quality Indicator

by Hayley Templar
BIOL/WATER 361, Fall 2012

Key taxa: Annelida, Clitellata, Oligochaeta, Naididae, Tubifex

Aquatic oligochaetes are known for their use as water quality indicators, especially in areas with urban and sewage effluent. In particular, the oligochaete species Tubifex tubifex is used as a water quality indicator because of its ability to tolerate low oxygen conditions, the presence of heavy metals, and other environmental conditions. This essay will discuss the tolerance of T. tubifex to specific environmental conditions, why this allows them to be widely used as a water quality indicator, and give examples of how T. tubifex and similar aquatic oligochaetes are being studied and applied as informative water quality indicators.

The species Tubifex tubifex belongs to the Phylum Annelia and is classified under the Class Clitellata, Subclass Oligochaeta, Order Tubificida, and Family Tubificidae (= Naididae). Aquatic oligochaetes are found mainly in the sediment of lakes and streams. Species of the Family Tubificidae are often dominant in depths greater than one meter in poorly oxygenated water. In the deep waters of lakes and in streams and rivers that are polluted with sewage, is where they are recorded to have the highest concentrated populations (Smith 2001). Tubifex spp. are known to inhabit organically polluted waters in addition to sewage settling tanks and trickling filters. They often thrive in water that is 10 to 60 percent saturated with oxygen. Oddly, Tubifex spp. have been seen to exhibit negative aerotaxis, meaning that they actively migrate from areas of high dissolved oxygen to areas of low dissolved oxygen, the opposite reaction of most aquatic organisms (Smith 2001).

Chapman et al. (1982) studied the tolerance of 12 oligochaete species, including T. tubifex, to specific pollutants and environmental factors. T. tubifex was found to be one of the most tolerant species to temperature and salinity. It was also the second most tolerant to anoxia, surviving an average of 16 days. Other studies have found that Tubifex species were able to survive anaerobic conditions for 48 days and after about 120 days of no oxygen small populations remained (Smith 2001). Though very tolerant to low oxygen conditions, it seems that Tubifex spp. cannot survive indefinitely in anoxic conditions. Dissolved oxygen is a very important water quality indicator. Rivers, streams, and lakes with very low oxygen generally have low aquatic organism diversity, have lower populations of desirable species such as fish, and have a lower aesthetic value. Dissolved oxygen is a problem in bodies of water that have organic pollution such as urban effluent and sewage. Because of the high tolerance of T. tubifex to low dissolved oxygen, as well as the tendency to migrate towards and thrive in low oxygen conditions, it is the perfect indicator species of organic pollution that may be causing low dissolved oxygen levels.

The tolerance of Tubifex tubifex to low dissolved oxygen is relatively well known; however, it may have the ability to tolerate other indicators of polluted water such as the presence of heavy metals. Lucan-Bouché et al. (1999) studied T. tubifex in a retention basin that contained runoff from a vineyard. Runoff from vineyards often contain high levels of the metals copper and lead, and T. tubifex were observed to be prevalent in this contaminated retention basin. Experimental contaminations with copper and lead were done to see how the worms reacted. It was found that when exposed to high concentrations of these metals, the worms lost their posterior parts (tails). Metal determinations done on the anterior and posterior ends of the contaminated T. tubifex found higher concentrations in the posterior ends. It was concluded that T. tubifex may accumulate concentrations of these metals in their posterior parts and then lose these parts to protect themselves from contamination. This interesting study illuminates the possibility of the use of T. tubifex as an indicator of copper and lead pollution. Because of the ability of these worms tosurvive high concentrations of these metals by losing their posterior parts, T. tubifex could prove to be an important indicator of contaminated water. There is potential to use the loss of the posterior parts as a biomarker for lead and copper contamination.

Bouché et al. (2000) came up with similar results by studying Tubifex tubifex tolerance to cadmium. The ability of T. tubifex to accumulate cadmium, as well as the toxicity of cadmium to this worm was studied. Acute toxicity was analyze by exposing the worms to 96 hours of daily renewal tests to cadmium solutions, and determining the dose that was lethal to 50% of the worms, as well as recording daily survival rates. T. tubifex was observed to lose its anterior parts (tails) when exposed to high concentrations of cadmium. Bioaccumulation studies showed that cadmium was rapidly taken up by the worm, suggesting some sort of an efficient detoxification method. These results show that T. tubifex can potentially be used as a water quality indicator of cadmium, due to its ability to accumulate the metal. The loss of the posterior parts could be used as a biomarker for cadmium contamination as well as copper and lead. Heavy metals are a big water quality concern, as they can be dangerous to human health. T. tubifex has a lot of potential to be an indicator of heavy metal pollution in lakes, rivers, and streams. Because these worms are able to accumulate high concentrations of copper, lead, and cadmium before they lose their posterior parts, this can be an important indication that the water is polluted and poses a potential risk to human health.

In addition to a tolerance of low dissolved oxygen and heavy metals, there are several other water quality indicators that Tubifex tubifex could be used evaluate. For example, T. tubifex is one of the more tolerant oligochaete species to temperature, salinity, and both high and low pH (Chapman et al. 1982). These are all important water quality parameters that can be indicative of pollution such as sewage and urban runoff.

Not only is there so much potential for the use of Tubifex tubifex and other aquatic oligochaetes as water quality indicators, but they are already being applied in a number of ways. Chapman (2001) described the usefulness of aquatic oligochaetes in creating Ecological Risk Assessments (EcoRA). They are most widely used for toxicity tests because they are easiest to culture and reproduce consistently. However, aquatic oligochaetes have recently been used less by researchers for pollution assessments because of their perceived over-tolerance to pollution. Some of the perceived difficulties with using aquatic oligochaetes for risk assessments are that they are difficult to handle, they are too fragile, they are difficult to find in sediments, they decompose quickly after death, and they are difficult to weigh due to attached sediments. Although these are difficulties that may be faced by researchers using aquatic oligochaetes in their studies, there are now many ways that these difficulties can be overcome. Species can be chosen based on their robustness and ease of use in the laboratory. Collection and preservation methods can also be modified to enable easier collection and preservation of target aquatic oligochaetes. Special techniques are also available for the removal of attached sediments, or analytical correction can be applied with evaluating the weight of the organisms.

Ingersoll et al. (1995) evaluated toxicity and bioaccumulation methods and applications of several aquatic oligochaetes, including Lumbriculus variegatus and Tubifex Tubifex. It was concluded that both of these aquatic oligochaete species were easy to use in the laboratory and easy to identify. It was also concluded that they have ecological importance because of their wide geographic distribution and tolerance to different sediments. Laboratory toxicity responses were confirmed by benthic population studies. T. tubifex in particular has been used in a variety of studies for a number of biological assessments such as acute toxicity, chronic toxicity, and bioaccumulation. They are also one of the major aquatic oligochaete species used in these types of assessments as benthic indicators (Chapman 2001). Overall, Chapman (2001) concluded that if aquatic oligochaetes are assessed as part of the benthos without preconceived, and often incorrect, assumptions about their over-tolerance, they provide most of the useful information for ecological assessments. For example, Lin et al. (2008) evaluated the relationship between aquatic oligochaetes and sewage pollution using statistical methods. A positive correlation was found between the abundance of oligochaetes and the River Pollution Index (RPI). It was concluded that aquatic oligochaetes are sensitive enough to provide a supplement for the regional urban pollution assessment applications for biotic indicators at the species-level. This is an example of how aquatic oligochaetes are being successfully used. Aquatic oligochaetes can be very useful indicators for water quality parameters such as sewage effluent, and they prove to be descriptive enough to use in urban pollution assessments and planning.

Aquatic oligochaetes, especially the species Tubifex tubifex, can be very telling indicators of water quality. They have an amazing tolerance for a number of water quality parameters, yet they have proven to be sensitive enough to be valuable in pollution assessments. Not only are they able to tolerate anoxic conditions for long periods of time, but they are able to accumulate large concentrations of some of the most toxic heavy metals. They have also proven to be tolerant of temperature fluctuations, salinity, and both highly acidic and basic water. The best water quality indicator organisms tend to abundant in the worst living conditions, and T. tubifex definitely proves to be just that. It is no wonder that they are found in the most stagnant, sewage polluted waters. T. tubifex not only is found in polluted waters, but is often abundant and thriving. They have been successful additions to Ecological Risk Assessments in the United States, River Pollution Indexes in Taiwan, and many other urban pollution assessments and regional studies. T. tubifex will surely continue to be an important indicator species for the most polluted waters and continue to help researchers and regulators determine the health of rivers, streams, and lakes across the world.

References Cited

• Bouché, M.-L., Habets, F., Biagianti-Risbourg, S. & G. Vernet. 2000. Toxic effects and bioaccumulation of cadmium in the aquatic oligochaete Tubifex tubifex. Ecotoxicology and Environmental Safety. 46: 246-251.
• Chapman, P.M. 2001. Utility and relevance of aquatic oligochaetes in Ecological Risk Assessment. Hydrobiologia. 463: 149-169.
• Chapman, P.M., Farrell, M.A., & R.O. Brinkhurst. 1982. Relative tolerances of selected aquatic oligochaetes to individual pollutants and environmental factors. Aquatic Toxicology. 2: 47-67.
• Ingersoll, C.G., G.T. Ankley, D.A. Benoit, G.A. Burton, F.J. Dwyer, I.F. Greer, T.J. Norberg-King, & P.V. Winger. 1995. Toxicology and bioaccumulation of sediment-associated contaminants with freshwater invertebrates: a review of methods and applications. Environmental Toxicology and Chemistry. 14(11): 1885-1894.
• Lin, K.-J. & S.-P. Yo. 2008. The effect of organic pollution on the abundance and distribution of aquatic oligochaetes in an urban water basin, Taiwan. Hydrobiologia. 596: 213-223.
• Lucan-Bouché, M.-L., Biagianti-Risbourg, S., Arsac, F., & G. Vernet. 1999. An original decontamination process developed by the aquatic oligochaete Tubifex tubifex exposed to copper and lead. Aquatic Toxicology. 45: 9-17.
• Smith, D.G. (2001). Pennack’s freshwater invertebrates of the United States (4th ed.). New York, NY: John Wiley & Sons, Inc.