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Concentrated CaCl2 and CaBr2 salt solutions of densities up to 2.3 kg L-1 are regularly used to control hydrostatic pressure in oil wells during special operations in the exploration and production of natural gas and crude oil. Various concentrations of high density salts are frequently left in mud pits near the drilling site as waste, polluting fresh and ground waters by spillage and drainage. The toxic effects of these salts have already been observed. This study investigated the effects of CaCl2 and CaBr2 on water flea Daphnia magna Straus in a 21-day reproduction test. The three tested concentrations of CaCl2 (240, 481, and 1925 mg L-1) caused a significant dose-response decrease of reproduction (p

High density brines are concentrated salt solutions which are regularly used to control the hydrostatic pressure in oil wells during special operations in exploration and production of natural gas and crude oil [1]. Calcium, sodium, potassium, magnesium and zinc chloride and bromide are most usually used as workover high density fluids, in quantity of 5 – 20 m3 per well [2]. Various concentrations of high density brines are left in the mud pits nearby the drilling site as waste and may pollute fresh and ground waters by spilling over and drain off through the ground. Investigating the effects of that kind of pollution was necessary, so a more extensive laboratory research of the toxic effects of high density brines on several test organisms (Lemna minor L., Daphnia magna L. and Allium test) was carried out before. The research results of the effect of sublethal concentrations of calcium chloride and calcium bromide and their mixtures 1:1 on the survival, growth and fecundity of the freshwater snail Planorbarius corneus L. showed a considerable dose-response decline of the survival, growth and fecundity [3]. In this study the effect of lethal concentrations of calcium chloride and calcium bromide (5985 ppm CaCl2 and 7939 ppm CaBr2) on the tissues of Planorbarius corneus L. was investigated. Histological samples were prepared by fixing the tissues with Bouin's solution (saturated picric acid, glacial ethanoic acid and formalin), imbedding in paraffin and sectioning between 6-8 μm. Samples were then stained using hemalaun-eosin [4]. The prepared samples showed no obvious histopathological changes except widening of hemolymphatic area in some organs (excretory organ, mantle cavity, osphradium, salivary gland) in comparison to the control (Figures 1 and 2). It was concluded that hyperosmotic medium caused a higher hemolymph viscosity and slower flow thus accumulating hemolymph in the hemolymphatic area and causing observed expansions.

Koncentrirane otopine kalcijeva klorida, kalcijeva bromida i njihove smjese (otežane vode) redovito se koriste za kontrolu hidrostatskog tlaka u naftnim bušotinama. Ovisno o uvjetima rada za jednu bušotinu potroši se 5-20 m3 otežane vode. Otežane vode u raznim koncentracijama ostavljaju se u isplačnim jamama uz lokaciju bušenja kao otpad te mogu onečistiti površinske i podzemne vode prelijevanjem u okoliš ili prodorom u podzemlje kroz tlo. Istraživanje takve vrste onečišćenja pokazalo se nužnim te je već poduzeto opsežnije laboratorijsko istraživanje toksičnosti otežanih voda na više test organizama (Lema minor L., Allium ascalonicum). Cilj ovog rada je istraživanje kronične toksičnosti subletalnih koncentracija kalcijeva klorida i kalcijeva bromida – otežanih voda i njihove 1:1 smjese na preživljavanje, rast i razmnožavanje slatkovodnog puža Planorbarius corneus L. Puž Planorbarius corneus L. odabran je za testiranje toksičnosti kao autohtona i česta vrsta u područjima istraživanja i proizvodnje nafte i plina. Ovaj rad obuhvaća i istraživanje učinka otežanih voda na drugu generaciju puževa izleženih u toksičnim koncentracijama tih kemikalija, komparativnu toksičnost na vodenbuhu Daphnia magna Straus, mjerenje apsorpcije kalcija iz kontrolne vode i test otopina. Dobiveni rezultati pokazali su smanjenje preživljavanja, rasta i plodnosti puževa u ovisnosti o koncentraciji toksikanata. Ovi rezultati ukazuju da bi stalna prisutnost različitih koncentracija otežanih voda u stajaćim vodama mogla utjecati na brojnost i distribuciju vrste Planorbarius corneus L. (zbog smanjenja broja jajašaca).

IN INA-Naftaplin laboratory, the extensive investigations on "heavy brines", which are used in oil industry as concentrated solutions of CaCl2 (481.3 gdm-3), CaBr2 (1065.9 gdm-3) and their 1:1 mixture, have been carried out. In this study, the effect of several concentrarions of heavy brines' water solutions to the fecundity and mortality of the second generation of fresh-water snail Planorbarius corneus L., hatched and raised in the same concentrations, was observed. The attempt was made to establish whether the permanent presence of various heavy brines' concentrations in stagnant water increases the toleration threshold to the chemicals, or their adverse effect in the second generation is stronger. The results suggest, that there is a possibility of adaptation of the population of snails permanently exposed to the diluted heavy brines' in stagnant water, since in higher concentrations of tested chemicals (CaCl2 1%, CaBr2 0.5% and the mixture CaCl2/CaBr2 1:1 0.5%) the differences in eff-masses production and in mortality rates between the first and the second generation of snails were significantly expressed (P -0.05).

Concentrated solutions of MERCK chemicals, calcium chloride and calcium bromide, being cleaner than technically prepared solutions were used in this study. Concentrated splutions of these chemicals and their mixture are regularly used to control the hydrostatic pressure in oil wells. The toxicity of some sublethal concentrations of these chemicals and their mixture to the fecundity, mortality and growth of the Planorbarius corneus L. has been researched. During the chronic exposure (six weeks) in all different concentrations of these toxicants, a reduced fecundity was revealed, at a slover speed in the test solutions then in the controls with standard water. The rate, for which reason the test was interrupted after five weeks. A higher mortality was ascertained in other tests then in the controls. All chages were formed to be reversible when the snails were no longer exposed to the action of the toxicants.