Aquatic Toxicology 78 (2006) 15–20 Bioaccumulation of cadmium in an experimental aquatic food chain involving phytoplankton (Chlorella vulgaris), zooplankton (Moina macrocopa), and the predatory catfish Clarias macrocephalus × C. gariepinus Suneerat Ruangsomboon a,∗ , Ladda Wongrat b a Faculty of Agricultural Technology, King Mongkut’s Institute of Technology Ladkrabang, Chalongkrung Road, Bangkok 10520, Thailand b Faculty of Fishery, Kasetsart University, Bangkok 10900,Thailand Received 5 October 2005; received in revised form 16 December 2005; accepted 24 January 2006 Abstract The accumulation of cadmium (Cd) was studied in an experimental aquatic food chain involving the phytoplankton Chlorella vulgaris as the primary producer, the zooplankton Moina macrocopa as the primary consumer, and the catfish Clarias macrocephalus × Clarias gariepinus as the secondary consumer. C. vulgaris was first exposed to Cd solutions at 0.00, 0.35, and 3.50 mg l -1 , referred to as control group and experimental groups 1 and 2, respectively. Subsequently, each group was fed to three corresponding groups of M. macrocopa. Finally, three groups of catfish were fed these corresponding groups of M. macrocopa. After C. vulgaris was exposed to 3.50 mg l -1 Cd (experimental group 2), the residual Cd in solution was only 4.01 gl -1 , lower than the maximum allowable limit of Cd in natural water sources (5 gl -1 ). Cd concentrations in C. vulgaris were 0.01 ± 0.00 gg -1 (dry wt) in the control group, 194 ± 1.80 gg -1 (dry wt) in experimental group 1, and 1140 ± 20.06 gg -1 (dry wt) in experimental group 2. The Cd concentrations in M. macrocopa were 0.01 ± 0.00 gg -1 (dry wt) in the control group, 16.48 ± 2.23 gg -1 (dry wt) in experimental group 1, and 56.6 ± 3.23 gg -1 (dry wt) in experimental group 2. The Cd concentrations in catfish muscle increased with increasing Cd concentrations in the food. After 60 days of fish culture, the mean concentrations of Cd in fish muscle were 0.01 ± 0.00 gg -1 (dry wt) in the control group, 0.61 ± 0.02 gg -1 (dry wt) in experimental group 1 and 1.04 ± 0.06 gg -1 (dry wt) in experimental group 2. Cd concentration in fish muscle of experimental group 2 was equal to the permissible limit. Cd accumulation affected fish growth: at the end of the study, the mean fresh weight (12.81 g) of catfish in the control group, was significantly higher than those experimental group 1 (10.43 g) and experimental group 2 (10.00 g). The results showed that the measurement of Cd concentration in water does not necessarily give a measure of the safety of aquatic organisms as human food. Hence, heavy metal contamination is a matter for concern when organisms are harvested, for fish and human consumption, from natural water sources. © 2006 Elsevier B.V. All rights reserved. Keywords: Cadmium; Bioaccumulation; Aquatic food chain; Chlorella vulgaris; Moina macrocopa; Catfish 1. Introduction The presence of heavy metals in the environment is partially due to natural processes, but is mostly the result of industrial waste (Mansour and Sidky, 2002). Contamination of aquatic ecosystems with heavy metals has increased worldwide. Cad- mium (Cd) is a toxic heavy metal, a contaminant mainly of aquatic ecosystems. It has many industrial uses, such as in Cd ∗ Corresponding author. Tel.: +66 2 326 4099; fax: +66 2 326 4099. E-mail address: krsuneer@kmitl.ac.th (S. Ruangsomboon). batteries, anti-corrosive coating of metals, pigments, and stabi- lizers for plastic (Stoeppler, 1991). The amount of Cd used in industry is increasing. When Cd contaminates the aquatic ecosystem, it can enter the aquatic food chain through direct consumption of water or biota; and through non-dietary routes such as absorption through epithelia. For fish, the gills, skin, and digestive tract are potential sites of absorption of Cd in water. Fish are often at the top of the aquatic food chain and may concentrate large amounts of Cd from the water. Toxic responses in fish exposed to elevated waterborne Cd are well documented. However, studies on oral exposures are sparse (Heath, 1995; Handy, 1996), even though 0166-445X/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aquatox.2006.01.015