Accumulation kinetics of arsenic in Daphnia magna under different phosphorus and food density regimes

Abstract

In the present study, the dissolved uptake, dietary assimilation, and elimination of arsenic (initially added as arsenate) in the freshwater cladoceran Daphnia magna were examined. A biphasic correlation between the arsenic uptake rate and its ambient concentration, as well as a two-saturation-site arsenic uptake competition with phosphate was observed. The calculated uptake rate constant, as influenced by the ambient phosphorus concentration, ranged from 0.035 to 0.35 L/g/d. Food concentration substantially decreased (by 23.2-64.4%) the arsenic assimilation efficiency with the incipient limiting algal food concentration of 3.86 mg/L dry weight. Arsenic assimilation by the daphnids was independent of their own phosphorus status, but was lower when their algal diet was phosphorus-limited and thus contained a higher proportion of arsenite due to the enhanced biotransformation. Arsenic efflux rate constant ranged from 0.34 to 0.44 d(-1) with increased food concentration slightly facilitating its loss. Excretion, accounting for 51.3 to 60.6% of total loss, was the dominant pathway for arsenic elimination with a remarkable contribution from offspring production (24.7-29.8%), whereas molting (3.64-4.05%) and egestion (7.9-11.9%) had minor roles only. According to the well-established biokinetic model, dietary assimilation was predicted to be the main pathway for arsenic bioaccumulation in the daphnids, and arsenic has a great potential to be biodiminished along the food chain.

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

“…Moreover, a favorable environment, rich in nutrients, could promote the formation of detoxifying agents, such as metallothionein, binding to arsenic ions, which makes this ametal unavailable (Miao et al 2012). 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.…”

“…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.…”

“…Several studies have tried to identify this ametal toxicity, isolated or associated with other metals, to aquatic and terrestrial organisms (Styblo et al 2000, Lyn Patrick 2003, Levy et al 2005, Norwood et al 2007, Liao et al 2008, Fikirdeşici et al 2012, Miao et al 2012, Zou et al 2013. Furthermore, mitigation and remediation actions in the environment have been used in processes involving precipitation or adsorption of this ametal mainly to oxides and hydroxides iron (Meng et al 2002, Zaw and Emett 2002, Fernandes-Machado and Miotto-Bigatão 2007.…”

“…Arsenic has high potential to bioaccumulate in animals and vegetables (Liao et al 2008, Miao et al 2012, exposed to man through ingestion of contaminated food. Thereby, evaluating arsenic toxicity to sensitive aquatic organisms is critical to preserve these ecosystems and to prevent contamination and bioaccumulation in humans.…”

“…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.…”