In developing a sediment bioassay protocol a number of propeties are desirable (DeWitt et al., 1989; Smith and Logan, 1993; Ingersoll, 1995) : (a) broad salinity tolerance; (b) high sensitivity to common sediment contaminants; (c) high survival rate under control conditions; (d) occupation of microhabitat(s) at or preferably, below the sediment-water interface to ensure maximum and consistent exposure to sediment contaminats; (e) low sensitivity to natural sediment variables, such as particle size and organic content, to allow a wide variety of sediment types to be tested; (f) broad geographic range to enhance the breadth of its application as a test species; (g) ease of collection, handling and maintenance in the laboratory; (h) ecological importance in estuarine systems; and (i) the ability to be cultured or year-round availibility from the field.  Ideally, a sediment toxicity test should also be rapid, simple and inexpensively (Luoma and Ho, 1993; Ingersoll, 1995).

See: Insecticide species sensitivity distributions: Importance of test species selection and relevance to aquatic ecosystems, Environmental Toxicology, DOI: 10.1897/04-025R.1. I hope this helps :-)

In developing a sediment bioassay protocol a number of propeties are desirable (DeWitt et al., 1989; Smith and Logan, 1993; Ingersoll, 1995) : (a) broad salinity tolerance; (b) high sensitivity to common sediment contaminants; (c) high survival rate under control conditions; (d) occupation of microhabitat(s) at or preferably, below the sediment-water interface to ensure maximum and consistent exposure to sediment contaminats; (e) low sensitivity to natural sediment variables, such as particle size and organic content, to allow a wide variety of sediment types to be tested; (f) broad geographic range to enhance the breadth of its application as a test species; (g) ease of collection, handling and maintenance in the laboratory; (h) ecological importance in estuarine systems; and (i) the ability to be cultured or year-round availibility from the field.  Ideally, a sediment toxicity test should also be rapid, simple and inexpensively (Luoma and Ho, 1993; Ingersoll, 1995).

Levent Bat has provided accurate information.

Many thanks Andrew. Will check it out.

Thanks Levent. So if a potential tox test species meets most of these requirements and performs (more or less) consistently for a given reference toxicity test, it can be regarded as a standard tox test organism for a given geographical area?

in addition to the criteria supplied by Levent Bat, you may want to read section 2 of the attached report.  I hope this is useful.  If more than one lab is to use the test, you may want to conduct a round robin study to see if results are similar between labs.  Meeting most of Levent Bat's requirements should qualify your species as a standard toxicity test organism for your area.   

Dear Ms. Ntuthuko,

 Dr. Levent and Dr. Doe have provided detailed description for the standard toxicity test organism. In addition I would like to emphasize that test-organism can be substance-specific or universal. In latter case it should have enough high sensitivity (less tolerance) not only to specific pollutant, but also to most types of local environmental pollution. This can be determined by acute or semi acute toxicity tests to several standard test-substances representing various types of pollution, e.g. salinization, eutrophication, heavy metals, pesticides, petroleum products, etc.

Many thanks to all for your valuable input.

My experience is below:

The broad aim of my studies was to evaluate the effects of specific contaminants of known concentration on two bioassay organisms Corophium and Arenicola which have been shown to have good potential for sediment toxicity testing and are likely to be used extensively in the future by regulatory agencies.  This was achieved by contamination of clean Ythan sediment with the heavy metals copper, zinc and cadmium.  Here I review the results of these experiments and draw some general conclusions about the potential of sediment toxicity tests in general.

I compared different protocols for estimating the metal concentrations in Corophium following exposing to sediment treated with copper, zinc and cadmium.  The study confirmed that if contaminated sediment in the gut was included in such analyses, then the apparent concentrations of these metals in Corophium would be elevated and it was recommended that either depuration in seawater or removal of the gut should be carried out before analysing invertebrates for metal burdens.  However, there are circumstances in which the levels could appear to be reduced, if clean sediment was in the gut, and this should be borne in mind when analysing animals collected from the wild in surveys.

See detail: Bat L, Raffaelli D, Marr IL. (1998). The accumulation of copper, zinc and cadmium by the amphipod Corophium volutator (Pallas). J. exp. mar. Biol. Ecol, 223 (2): 167-184.

Survival of Corophium decreased with increasing the metal concentrations in seawater both with and without sediment, but amphipods were less affected by the metals when the sediment was present.  These data indicated that amphipods were stressed in the absence of the sediment.  However, the presence of sediment did not affect body burdens, indicating that the metals were assimilated at a faster rate by Corophium in the presence of sediment since concentrations of metal in water might have been expected to be lower in the presence of sediment due to increased metal adsorption.  These findings have important implications for ecotoxicological work especially for the assessment of seawater (as opposed to sediment) toxicity.  It is clear that such tests must be conducted in the presence of sediment, otherwise any recorded effects may be due to stress rather than the toxicity of any contaminants present.

There were inverse relationships between the bioconcentration factors (BCF) and water concentrations and BCFs were always higher for dead than living Corophium for each metal.  When allowed to choose between clean and contaminated sediment, Corophium tended to burrow in clean sediment, avoiding contaminated sediment.  Avoidance of metal contaminated sediment may play a significant role in the field, because of Corophium’s ability to detect the presence of the metals in sediment and move away, thereby avoiding the full effects of contamination.

See detail: Bat L, Raffaelli D. (1999). Effects of gut sediment contents on heavy metal levels in the amphipod Corophium volutator (Pallas). Tr. J. Zoology, 23: 67-71.

When cadmium was added in combination with zinc, this reduced Corophium mortality and cadmium burdens were less.  In the field, sediments are contaminated with complex mixtures of chemicals and therefore more attention must be given to assess sediment toxicity when metals are complexed like this.  Indeed, this phenomenon demonstrates well the utility of the bioassay approach: straightforward chemical analyses of these sediments would have predicted a much greater impact on the organisms than is actually the case.  On the other hand, Corophium was highly sensitive to contaminated sediment from the river Odiel, Spain, containing a complex mixture of metals.  Thus, responses of amphipods to multiple contaminants are not often as straightforward to interpret compared with single contaminant exposures due to complex interactions between the chemicals, although such responses clearly demonstrate the real toxicity of the sediment and are to be preferred to chemical analyses in this respect.

See detail: Bat L, Raffaelli D, Marr I.L. (1996). Toxicity of river sediments in South-West Spain. E.Ü. Su Ürünleri Dergisi, 13 (3-4): 425-432.

Corophium was also very sensitive to the pesticide permethrin (the 28-day LC50 was 67 ng g-1).  In an inter-laboratory ring-test, the mean individual dry weight of Corophium increased with increasing permethrin concentrations, this becoming more significant at higher concentrations indicating progressive loss of smaller individuals.  Thus, it seems that juveniles are more sensitive than adults to this, and probably other contaminants, and this has implications for the use of mean individual dry weight as a sublethal endpoint in such bioassays.

See detail: Bat, L, Raffaelli, D. (1996). The Corophium volutator (Pallas) sediment toxicity test: An inter-laboratory comparison. E.Ü. Su Ürünleri Dergisi, 13 (3-4): 433-440.

The potential of the bioassay for assessing the quality of organically enriched sediment was assessed by a combination of field and laboratory experiments.  Whilst the results were not conclusive they illustrate the need for both laboratory and field bioassays, the results of each being complementary.  The organically enriched sediments had no significant effect on the survival, emergence from sediment and reburial ability of Corophium and this bioassay is probably not appropriate for estimating the toxicity of enriched sediments.

See detail: Bat L, Raffaelli D. (1998). Survival and growth of Corophium volutator in organically enriched sediment : A comparison of laboratory and field experiments. Tr. J. Zoology, 22 (3): 219-229.

Whilst the Corophium sediment bioassay showed a clear ecological response to metal contaminants, it might be misleading to estimate the ecological impacts of contaminated sediments without relevance to other species.  Therefore, the polychaete Arenicola was also used to assess sediment toxicity using the bioassay approach.  These experiments indicated that whereas cadmium was much more toxic than copper or zinc to Corophium, copper was much more toxic than zinc or cadmium to Arenicola. For the Arenicola bioassay, the number of casts produced and cast size (weight) were used as a sublethal test endpoint.  This was very sensitive: even at low concentrations the rate of cast production was reduced.  Interestingly, metal levels in casts were significantly less than in unworked sediment and a number of mechanisms may be responsible for this.

See detail: Bat L, Raffaelli D. (1998). Sediment toxicity testing: A bioassay approach using the amphipod Corophium volutator and the polychaete Arenicola marina. J. exp. mar. Biol. Ecol, 226: 217-239.

Several bioassay methods have been developed since the EPA/COE testing protocol was devised, involving a great variety of test species.  The amphipod Corophium volutator and the polychaete Arenicola marina are now beginning to be used routinely as standard bioassay organisms for assessing the toxicity of marine sediments for regulatory purposes (Thain et al., 1994; Roddie et al., 1994; Fleming et al., 1994), but little is known about the effects of specific contaminants on the bioassay response.  The present study has confirmed the potential of both species for sediment toxicity bioassays, both species meeting most of the criteria required (given by DeWitt et al., 1989) for suitable estuarine sediment toxicity test organisms.  These are a wide geographic distribution, ecological importance, high sensitivity to sediment contamination, broad salinity tolerance, ease of handling and maintenance in the laboratory, high survival under control conditions, year-round availability from the field and well-established, easily set up protocol.  However, there are some comparisons worth making between the two bioassays.  Both species are sensitive to metals, but this sensitivity is different for at least one, copper, Corophium being much less sensitive than Arenicola.  Thus for sediments predominately contaminated with copper, the two bioassays could produce conflicting results.  Clearly there is a need to carry out further single contaminant trials on these (and other) species to assess their suitability for detecting toxicity and also trials involving complex mixture of contaminants since it is likely that these too will generate different responses in the two species.  Finally, the two species differ in the resource demands they place on the experimenter.  Corophium is small, very abundant and only small volumes of test sediment are required.  In contrast, Arenicola occurs at much lower densities, requires much more effort to collect and the bioassay requires much larger volumes of test sediment, and hence equipment and laboratory space.  Nevertheless, there are clear advantages of the two bioassays as a mean of assessing sediment toxicity, and it is hoped that they will continue to be employed routinely in monitoring programmes for coastal waters.

Dear Levent.

Many thanks for sharing your experience. It is very relevant for what we want to achieve here in South Africa.

I agree with Dr. Doe and Dr. Levent’s last comments. Standard test organisms have to be calibrated in various labs situated in different regions. By this way invertebrate Daphnia magna was accepted as a standard test-organism for the water quality analysis.

I think the organism should not show hermaphroditism and the organism's niche should be broad enough.  Please follow http://dx.doi.org/10.1016/S0025-326X(01)00253-3 article. I think the authors described very well.

Often, model organisms are chosen on the basis that they are amenable to experimental manipulation. This usually will include characteristics such as short life-cycle, techniques for genetic manipulation (inbred strains, stem celllines, and methods of transformation) and non-specialist living requirements. Sometimes, the genome arrangement facilitates the sequencing of the model organism's genome, for example, by being very compact or having a low proportion of junk DNA (e.g. yeast, arabidopsis, or pufferfish).

When researchers look for an organism to use in their studies, they look for several traits. Among these are size, generation time, accessibility, manipulation, genetics, conservation of mechanisms, and potential economic benefit.

I think Levant Bat touched on many of the important factors for consideration. I would just emphasize one aspect though: culturing a laboratory testing population should be simple enough that any suitable facility is capable of doing so. That is to say, there should not be a single source for the test organism.

Many thanks for the useful comments. In a situation where the test can only be used by two laboratories that are located within the same region (this is a current situation in South Africa), but have sourced test organisms from different locations, would the round robin or calibration test still be valid (assuming that similar results have been obtained)?

It is possible to test. We did it. Please see attachment file

Best

Prof. Dr. Levent Bat

I agree with Levent Bat.  It would be best if the organisms could be obtained from the same area to reduce genetic variability, but not absolutely necessary since the two labs will presumably have different sources of the test species when doing their operational testing.  You will need to include clean and contaminated sediments in the round robin test.