Arch. Environ. Contam. Toxicol. 19, 84-93 (1990) E Archives of nvironmental c ontamination 9 1990 Springer-Vedag New York Inc. Metal Concentrations and Tissues Distribution in Larvae of Chironomus with Reference to X-ray Microprobe Analysis G. Krantzberg* and P. M. Stokes** *Ontario Ministry of Environment, Great Lakes Section, 1 St. Claire Ave W., Toronto, Ontario M4V 1P5, **Institute for Environmental Studies and Department of Botany, University of Toronto, Toronto, Ontario, Canada M5S 1A4 Abstract. Atomic absorption, scanning electron microscopy and x-ray microprobe analysis were used to examine metal accumulation and localization in larval chironomids col- lected from two sites that differed in their extent of contami- nation. Lead, Fe, Cd, Cu, Ni, Zn, and occasionally, A1 were detected in the midgut and anal papillae of chironomids, with the greatest frequency of detection occurring in the midgut of larvae collected from the more heavily contami- nated site. Metal storage differed between the populations studied. Eighty-one percent of the spectra that had metals in detectable concentrations were of larvae from the contami- nated site, while only nineteen percent were from the less contaminated site. Sixty percent of the spectra were from the midgut and fifteen percent were from the anal papillae of the contaminated population. Nine percent of the remaining spectra were from the midgut and nine percent were from the anal papillae of chironomids from the less contaminated site. For some elements, differences in metal storage be- tween populations were suggestive of differences in metal tolerance. To predict the effects of trace metals on biota, it is important to determine the relationships between metal concentrations in the environment and those in biological tissues. In cases where organisms can regulate metals, correlations between environmental concentrations and concentrations in these organisms would be poor. Tolerance to elevated concentra- tions of trace elements can involve the exclusion, active ex- cretion, or intracellular storage of metals. The ability of many invertebrate species to produce metallothioneins, to package metals in membrane-bound vesicles and to localize metals in specific tissues has been widely reported (Brown 1977; Boilly and Richard 1978; Fischer et al. 1980). In gen- eral, metal-containing granules tend to be associated with organs involved in digestion, storage, ion regulation and ex- cretion (Brown 1982). For example, the chloragogenous tissues of annelids, which have been identified as sites for metal storage, are comparable to the vertebrate liver (Back 1983). Lead and Cd in tubificids are stored in the chloragogen tissues of the ante- rior portion of the organism (Prosi et al. 1983), Zn and Pb in the hind gut (Back 1983) and in the midgut glands of oligo- chaetes (Prosi 1983; Prosi and Back 1985). In crustaceans, metal storage also occurs in the hepato- pancreas of isopods (Brown 1978), an organ that is believed to be important in metal detoxification (Brown 1978; Olafson et al. 1979). Intracellular inclusions of Cu, Pb, and Fe in isopods have been reported (Brown 1977; Alikhan 1972; Wieser 1968; Lyon et al. 1983), and sulfur-metal com- plexes were found in Cu and Pb tolerant aquatic isopods (Brown 1977). X-ray microanalysis of the midgut parenchyma tissues of the barnacle Balanus balanoides indicated the presence of Mg, P, K, Ca, Fe, Cu, and particularly Zn in granule-rich pellets. Neither Mn nor Pb were detected, despite their pres- ence in the environment (Walker et al. 1975; Walker 1977). Copper and Zn have been detected in granular amoebo- cytes of molluscs, particularly those of the gut and kidney (Romeril 1971; Ruddell 1971; George et al. 1984). Zinc and Cu have also been detected in oyster gills (George 1983). For scallops, Cd, Ag, Mo, Br, Zn, Cu, and A1 were stored in the digestive cells (Ballan-Dufrancais et al. 1985). Metal localization has been studied in several insect taxa. Copper containing cytolysosomes were detected in the midgut epithelium of larval Drosophila where cuprophilic cells increased in size and number with increased concen- trations of dietary Cu (Filshie et al. 1971). Using x-ray mi- croanalysis, Tapp (1975) examined the Cu-containing lyso- somes of the Drosophila midgut epithelium and described granules that contained Cu and S and, less frequently, Zn and P (Tapp and Hockaday 1977). Metal-binding proteins have been described for insects. Synthesis of low molecular weight Cd-binding proteins in response to exposure to ele- vated Cd concentrations has been induced in fleshflies (Aoki et al. 1984), stoneflies (Everard and Swain 1983) and midges (Yamamura et al. 1983). Marshall (1983) suggested that in larval homopterans, Cu is bound by a metallothionein-like protein in the fat body cells, important sites for nutrient storage. Histochemical and ultrastructural evidence reveal that metals can be concentrated into specific storage units that are generally associated with digestion, excretion, or ionic