Biokinetics and tolerance development of toxic metals in Daphnia magna

Abstract

Abstract-Daphnia magna is widespread in many freshwater systems of temperate regions and frequently is used to test metal toxicity. Recently, studies have been performed to determine metal biokinetics and development of tolerance in this important zooplankton species. In the present paper, we review the recent progress in these areas and suggest possible directions for future studies. Substantial differences exist in aqueous uptake, dietary assimilation, and elimination of several metals (Cd, Se, Zn, Ag, Hg, and MeHg) by D. magna. The routes of uptake are metal-specific, with Se and MeHg being accumulated predominantly through diet. All metals except Ag can be biomagnified from algae to D. magna, providing that metal concentrations in algae and algal food density are relatively low. Methylmercury is biomagnified in all situations. As a route for metal elimination in D. magna, maternal transfer is especially important for Se, Zn, and MeHg. On the other hand, the effect of single-generation exposure to metals on D. magna is very different from multigeneration exposure, which often results in a significantly higher metal tolerance. Moreover, D. magna easily loses metal tolerance developed through long-term exposure. Recovery from metal stress can temporarily increase the sensitivity of D. magna to metal toxicity. Finally, metallothionein-like protein is responsible for minimizing metal toxicity in D. magna. The results inferred from these studies can be extrapolated to other aquatic invertebrates as well as to other pollutants in the aquatic environment.

Arsenic toxicity to cladocerans isolated and associated with iron: implications for aquatic environments

“…However, organic matter, derived from the diet, may not have an important role as a chelator, considering the organisms of these tests, which are filter feeders. Furthermore, filtration activity can be changed in the presence of food, reducing passage times of both food and ametal, reducing their absorption by this test organism (Tsui and Wang 2007), the hypothesis more plausible for the present study.…”

“…Furthermore considering the chitin constitution of cladocerans carapace, the toxicity of arsenic may be enhanced by adsorption of this ametal to exoskeleton of test organisms, and iron could increase this adsorption, although some authors associate the metal adsorption to limestone from carapace (Tsui and Wang 2007). Carney et al (1986) assessed cadmium uptake in Daphnia magna and found that most of this metal was adsorbed to the shell bodies, and tolerance was related to molting.…”

“…For many authors, metallothioneins are produced in situations of stress, such as contamination by metals, and play a key role in reducing toxicity of selenium, cadmium, zinc, copper, silver and arsenic among others (Cousins 1983, Kägi and Schäffer 1990, Roesijadi 1992, Amiard et al 2006, Tsui and Wang 2007, Nordberg and Nordberg 2009, Miao et al 2012. Bodar et al (1990) reported a temporary cadmium tolerance in Daphnia magna by the production of metallothionein.…”

“…The reduction of metals assimilation in Cladocera can also occur through excretion, molting, and even by transfer from mother to neonate (Tsui and Wang 2007). Miao et al (2012) found that arsenate bioaccumulation in D. magna was reduced under high food availability and there was loss of arsenic incorporated by ecdysis (4%), excretion (12%) and transfer to the neonate (30%).…”

“…Cladocerans are in the transition zone in aquatic food chains, between producers and secondary consumers, and can be considered essential to transfer metals through the trophic chain (Tsui and Wang 2007), being used in ecotoxicological studies about arsenic toxicity (Yu and Wang 2002, Fikirdeşici et al 2012, Miao et al 2012.…”