Magna form

The minuta and magna forms excreted in the faeces in intestinal amoebiasis are usually not infectious, as they perish rapidly in the stools once they have been excreted. Today, differentiation can be made between the two forms using molecular biology techniques. Only the cysts are responsible for transmission, but they are not present in the stool in the acute phase infection from the cysts is transmitted by the faecal-oral route and hence only in the symptom-free, chronic stage of the disease. An exact incubation period has not been defined. The latent period may last for several years. 

Irgolic, K.J., E.A. Woolson, R.A. Stockton, R.D. Newman, N.R. Bottino, R.A. Zingaro, P.C. Kearney, R.A. Pyles, S. Maeda, W.J. McShane, and E.R. Cox. 1977. Characterization of arsenic compounds formed by Daphnia magna and Tetraselmis chuii from inorganic arsenate. Environ. Health Perspec. 19 61-66. 

Cerejeira, M.J., Pereira, T. and Silva-Femandes, A. (1998) Use of new microbiotests with Daphnia magna and Selenastrum capricornutum immobilized forms, Chemosphere 37 (14-15), 2949-2955. 

If the chemical composition of the samples is known or at least partly known (in a stepwise TIE approach) or existing data allow for QSAR calculation, the samples can be ranked by TUs. Arts et al. (2006) studied, in 12 outdoor ditch mesocosms, the effects of sequential contamination with 5 pesticides in a regression design. They applied dosages equivalent with 0.2%, 1%, and 5% of the predicted environmental concentration (PEC) subsequently over 17 weeks. Endpoints recorded over 30 weeks included community composition of macroinvertebrates, plankton, and macrophytes, and leaf litter decomposition as functional ecosystem parameters. TUs were calculated in relation to acute toxicity data for the most sensitive standard species Daphnia magna and Lemna minor. Principal response curves (PRCs), a special form of constrained PCA, and Williams test (NOEC, class 2 LOEC) were used to identify the most sensitive taxa. Next to direct effects on certain species, also indirect effects, for example, how the change in abundance of a sensitive species affects the abundance of another, more tolerant species, can be detected only in mesocosm or in situ experiments. All observed effects were summarized in effect classes in a descriptive manner. 

Other metal cations that may form complexes with the toxicant may have a profound effect on toxicity. The toxicity of ethylenedi-amine tetraacetic acid (EDTA) and diethylenetriamine pentaacetic acid (DTPA) and their metal complexes has been examined in daphnids. The results are relevant both for the effect on the toxicity of metal cations and for the influence of complexation on these toxicities. For the acute toxicity (ECS0, 24 h) to Daphnia magna, the following results (mg/1) were obtained (Sorvari and Silanpaa 1996) ... 

Toxicology SI. skin irritant in cone, form, non to very si. irritant 1% si. to mod. eye irritant (undiluted) dust inh. may cause coughing, mucous prod., shortness of breath TSCA listed Environmental LC50 (daphnia magna, 96 h) 168-280 mg/l nonbiodeg. removed with the biomass in typ. wastewater treatment... 

Daphnids (water fleas) occur ubiquitously in aquatic ecosystems and, as primary consumers, they form an important link in aquatic foodwebs. The standard species Daphnia magna, which can be cultured in the laboratory, is used in toxicity tests to record adverse effects on the survival (acute, 48 h tests) or the growth and reproduction (chronic, 21 d tests) of the animals. The toxicity is generally described in terms of the EC5Q (EC effective concentration) that is, the level of the toxicant (mg/1) which affects 50% of the individuals exposed, regardless of how the effects are evoked. A variety of factors may considerably influence the absolute values of the observed toxic concentrations ... 

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