This research paper aims to discuss the factors determining the toxicity of a compound to organisms in the natural environment. In bioassays, which are usually asked for in an ecological risk assessment process, the levels of toxicity are defined. The toxicity of a compound in organisms is basically caused by natural factors coined as "false positives" or "confounding factors." Examples of these are ammonia, sulfide, or grain size and not the actual contaminants present. Some of them will be discussed in the factual information part of this paper. A main goal of this paper is to evaluate these natural factors forming certain amounts toxicity or false positives; to define, discuss, and think of new methods task to measure or eliminate these harmful factors; and to specify and discuss standard and new low budgeted bioassays needed to conduct a sediment toxicity tests.
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Toxicogenomics - Toxicogenomics is a new growing field, which interlinks genomics and bioinformatics in order to define and classify the mechanisms of toxicity of compounds (Cavet, 2003). Aside from using porewater contaminants, part of the main tools utilized in toxicogenomics is the DNA microarrays. In this, a laboratory can use toxicity studies of organisms using several different compounds associated with hepatotoxicity of body internal organs. In turn the compounds can be observed with mechanisms like hepatic carcinoma, steatosis, cirrhosis, hypertrophy, DNA damage, phospholipidosis and necrosis to be able to know the hepatotoxic response of an organism.
Brief History of Toxicogenomics - Currently, environmental managers focused on for maintaining the natural environment with sediment assessment, policymakers, and scientists are still likely to lack knowledge in the factors that affect toxicity of compounds in organisms. The height of sediment assessment in the environmental field was only during the early 1990s. The first committees concerned that conducted firsts sediment bioassay guidelines was the American Society for Testing and Materials or ASTM and U.S. Environmental Protection Agency or EPA, also during the 1990 (Duckworth et al., 2000). Subsequent to them is the California State Water Control Board that sponsors the Bay Protection and Toxic Cleanup Program or BPTCP. It was also prominent in the environmental control scene at that time.
Ecotoxicology - Ecotoxicity is the shortened term for ecological toxicity and the 2 refer to the methodologies, models and the empirical results in studying the negative effects resulting from the natural or man-made substances to certain organisms, communities or ecosystems situated in the natural environment. There are a lot of tests relating to the basics of general toxicology in Ecotoxicology, since it is a branch of toxicology (2007 Copyright Nickel Institute).
Compounds Contributing to Toxicity of Organisms in A Natural Environment
Chloroform is a well-known drinking water disinfection used in products. It is not found to be hepatocarcinogenic in some studies on orgranisms with tested substance concentrations (Beaman et al., 2001). A chronic toxicity can be accounted when there is evidence in organisms with internal affecting organs like levels of gallbladder lesions and bile duct abnormalities. Just recently, U.S. Environmental Protection Agency (U.S. EPA) saw this compound to be harmful, "Are today's standards based on rodent megadose studies relevant to real world exposures?"
Depleted Uranium or DU is a by-product resulted from the enrichment process of the Earth's natural uranium (Fleming et al., 2006). If released into the natural environment, it can endow harm on humans and ecological health across the globe. The major hazard rendered by DU comes from its heavy metal dosage of toxicity and not from its radiologic amount of toxicity.
Ammonia is known as the total ammonia, which is the compound form of ammonium ion and un-ionized ammonia (Fleming et al., 2006). Its particles are results of certain bacterial actions happening during the decaying stage of an organic matter and are a natural process in form. Toxicity tests have been started on organisms to measure behaviour response to some contaminants of concern aside from a dosage of high ammonia.
Sulfide is a product of anaerobic decomposition process in organisms and can be greatly found in aquatic sediments (Fleming et al., 2006). It is more toxic than ammonia in particular conditions. It generates toxicity in 3: a toxicant by itself, by lowering the amount of metal toxicity through creating insoluble metal sulfide solids or metal sulfide complexes, and by harming animal behaviour, which in turn can change the toxicity of the sulfide and some sediment contaminants.
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Grain Size can also add confounding effects by means of its chemical and physical properties. The organisms that need particular substrate, when grain size is either too small or too large can be hurting to animals. Amphipods or worms can be found, which are sensitive to grain size and should be added to sediments found with a compatible grain size. Adding to this, the availability of contaminants can relate to the sediment grain size. Wherein, the fine grain sediments are generate more content of clay and organic carbon. This only shows an alarming bacterial activity. Hence, the mixing of these sediments can lead to added bioavailability and toxicity (Fleming et al., 2006).
High levels of total organic carbon or TOC is also associated with the fine grain sediment in toxicity (Fleming et al., 2006). For a fact, bacteria feed on organic matter, which results to chain of events like oxygen depletion and heightened sulfide ors ammonia. Yet, these are natural processes. However, they still are found to add natural toxicity due to man-derived means.
Simultaneously Extracted Metals/Acid Volatile Sulfides or SEM/AVS are bacteria situated in an organism, which can lower sulfate into sulfide, which can show high TOC levels leading to depleted dissolved oxygen (DO) and heightened ammonia levels. Yet, sulfide is basically found non-highly toxic, because there are marine worms, such as polychaetes, and fish, which are very tolerant to particular amounts of sulfide. Values of SEM/AVS that are <1.0 should be defining of a little toxicity amount, while values of >1.0 definitely prove toxicity (Fleming et al., 2006).
Dissolved Oxygen or DO is vital in sustaining a healthy test environment. It may act synergistically with some toxicants to be able to cut down the toxicity level through lowering the count of toxicants or in other cases to add metals in anoxic sediments (Fleming et al., 2006). The presence of Low DO can heighten toxic effects due to hypoxia.
Salinity can also be a crucial factor in organisms or sediment quality. Since it affects ammonia toxicity (Fleming et al., 2006).
Suggestion for Successful Toxicity Tests (Duckworth et al., 2000)
â€¢ Choose the appropriate species
â€¢ Transport fast, coolly, and with sediment
â€¢ Avoid handling stress
â€¢ Prevent chemical contamination
â€¢ Shun from temperature or salinity shock
â€¢ Adapt test organisms to test conditions, remove animals that do not meet survival criteria: > 15-20% mortality, rejected batch, and ask for another
â€¢ Feed if compulsory at some point in holding and acclimation
â€¢ Tests should be performed within a customary time period from day animal was given
(2-3 days for A. abdita)
â€¢ Employ the precise life stage for testing
â€¢ Constantly operate the entire necessary controls
â€¢ Read instructions carefully
Organisms and sediments are in nature affecting toxicity results, which, in turn, is not possible be reduced in terms of numerical values. To explain this further, for example, a required toxicant used in amphipod bulk sediment tests can lead to varied toxicity responses, but it depends on the pH, grain size, ammonia, salinity, total organic carbon, porewater volume, and ratio of the found extracted metals/acid volatile sulfide or SEM/AVS in a study. Part of the methods to treating toxicity is the ability of porewater contaminants to bind to organics and result to non-bioavailable factors leading in low amounts of or even no toxicity in organisms. Toxicity is a very vital issue in testing water quality.