Pergarnon zyxwvutsrqpo Environmental Toxicology and Chemistry, Vol 14, No 10, pp. 1687-1695, 1995 Copyright zyx 0 1995 SETAC Printed in the USA 0730-7268/95 $9 50 zyx + .OO 0730-7268(95)00123-9 zyxwvu Environmental zyxw Toxicology ACUTE TOXICITY OF HEAVY METALS FOR BENTHIC EPIPHYTIC FORAMINIFERA zyxwvut PARAROTALIA SPINIGERA (LE CALVEZ) AND INFLUENCE OF SEAWEED-DERIVED DOC VLADIMIR BRESLER and VALENTINA YANKO* Institute for Nature Conservation Research, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel (Received 12 May 1994; Accepted 22 February 1995) Abstract -The acute toxicity of cadmium, copper, and mercury to the benthic epiphytic foraminiferan Pararotaha spinigera (Le Calvez) was investigated using seven different vital cytophysiological and cytochemical methods. The ability to enzymati- cally hydrolyze the fluorogenic substrates fluorescein diacetate or fluorescein dibutyrate was the most sensitive method of LC50 value determination. The LC50 (24-h) values for cadmium, copper, and mercury determined by this assay with fluorescein di- acetate was 0.56, 1.4, and 0.07 pM, respectively. The content of seaweed-derived dissolved organic carbon (DOC), measured by absorbance at 436 nm, produced a dramatic increase of LC50 values for the heavy metals in a dose-dependent manner. “In- tact” epiphytic foraminifera attached to seaweeds are less sensitive to acute toxicity of cadmium, copper, and mercury than are “detached” foraminifera. Keywords-Epiphytic foraminifera Heavy metals Acute toxicity LC50 (24-h) DOC INTRODUCTION Numerous studies have demonstrated the importance of using various animal species to detect dangerous ecosystem contaminations [ 1-41. Species occupying a key position in the life of ecosystems would be useful biomonitors. Thus, the continual global biogeochemical cycles of inorganic and or- ganic compounds are regulated mainly by biological activ- ity of benthic communities, especially bacteria and protozoa [4-71. Freshwater protozoa play an important role in the uti- lization of carbon and nitrogen, the food web and the “mi- crobial loop” in both natural and wastewaters [4,8-lo]. These protozoa have evolved a variety of mechanisms for protec- tion from toxic chemicals, including heavy metals [ll-161. Therefore, freshwater protozoans have been used for ecotox- icological investigations [4]. Marine protozoa, especially foraminifera, play a signifi- cant role in global biogeochemical cycles of inorganic and or- ganic compounds, making them one of the most important animal groups on earth [10,17-191. Foraminifera have a shell that may remain a long time after their death; shell deposits have been used to determine former population structure, quantity of specimens, and environmental quality [ 10,17- 211. Benthic foraminifera dwell in the sediment, on sub- marine outcrops, coral reef, reef rubble, and mollusk shells, or as epiphytes on seaweeds or seagrass [17-191. Benthic, especially attached epiphytic foraminifera, ha- bituate under very complicated chemical conditions. Dis- solved organic carbon (DOC) has been reported in the sediment in concentrations of up to 40 g/L [22]. This DOC consists of humic acids, small alkyl carboxylic acids, and sim- *To whom correspondence may be addressed. ple aromatic acids as well as amino, nucleic, uronic, and muramic acids [23-251. Decomposition of seaweeds and sea- grass has been shown to produce DOC [26]. The sediment may also contain peptides, proteins includ- ing exoenzymes liberated by bacteria, a wide cluster of nat- ural microbial, algal or animal toxins [23,27-301, and various anthropogenic xenobiotics like heavy metals, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons [22,31,32]. The following defense mechanisms against xenobiotics were detected in benthic epiphytic foraminifera: (a) mucopolysac- charide coat that forms additive diffusion barrier and binds some cationic xenobiotics; (b) membrane carrier-mediated transport system for elimination of anionic xenobiotics from the cytoplasm; (c) active intralysosomal accumulation and isolation of some cationic xenobiotics; and (d) haloperoxi- dases that transform xenobiotics to their haloderivatives [33]. Benthic foraminifera, though rarely used, may be useful for ecotoxicological investigations and monitoring. As a first step in the research, this study was focused on the following problems: (a) selection and adaptation of some sensitive cytophysiological and cytochemical methods to de- tect and assess objectively foraminiferal responses; (b) de- termination of acute toxicity (LC.50) of cadmium, copper, and mercury for an epiphytic benthic foraminiferan, Para- rotalia spinigera; and (c) determination of the interaction of seaweed-derived DOC on the acute toxicity of these metals. The DOC may alter the toxicity of many anthropogenic xe- nobiotics including heavy metals [22,26,34-371. The application of test chemicals to indicate cytophysio- logical or cytochemical responses was complicated by the masking of the cytoplasm by the foraminiferal shell, render- ing simple vital microscopy ineffective. Both attached and “detached” foraminifera are sessile, with the pseudopodial 1687