The behaviour of the worms that escaped from sediment resulted in a reduction of their feeding activity, reproduction, and also mortality during the chronic test. The presence of ammonia at toxic levels in the artificial sediment during the first days after its preparation influences the quality of the water column and interstitial water, affecting the biological results of the test. The addition of supplementary food to the sediment at the beginning of the test is necessary to get satisfactory reproductive levels at the end of the 28-day chronic test, but this supplement of organic matter also provoked an additional increase of the levels of ammonia. In the present study, artificial sediment has been used with Tubifex tubifex (Tubificidae, Oligochaeta) in both culture and in 28-day toxicity tests with spiked toxicants, in order to avoid the presence of occasionally important concentrations of some pollutants in sediments from apparently clean sites. They usually inhabit the bottom sediments of lakes, rivers, and occasionally sewer lines and outlets.'The formulation and preparation of artificial sediments to be used in chronic toxicity tests is an important issue in the standardisation process. Encystment may also function in the dispersal of the worm. tubifex can survive drought and food shortage. By forming a protective cyst and lowering its metabolic rate, T. They can also survive in areas heavily polluted with organic matter that almost no other species can endure. The worms can survive with little oxygen by waving hemoglobin-rich tail ends to exploit all available oxygen, and can exchange carbon dioxide and oxygen through their thin skins, in a manner similar to frogs. Micro-plastic ingestion by Tubifex worms acts as a significant risk for trophic transfer and biomagnification of microplastics up the aquatic food chain.

These worms ingest sediments, selectively digest bacteria, and absorb molecules through their body walls. Tubifex probably includes several species, but distinguishing between them is difficult because the reproductive organs, commonly used in species identification, are resorbed after mating, and because the external characteristics of the worm vary with changes in salinity. Tubifex tubifex, also called the sludge worm or sewage worm, is a species of tubificid segmented worm which inhabits the sediments of lakes and rivers on several continents.

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