Evaluation of kraft wood pulp mill secondary effluent toxicity in Engraulis ringens and Strangomera bentincki embryos utilizing a developmental toxicity test

摘要

The anchoveta, (Engraulis ringens) and sardine (Strangomera bentincki), are coastal pelagic species found from central (29°S) to southern Chile (42°S). During their peak spawning season, winter to early spring, high egg concentrations are found in an important spawning area located off the coast of central southern Chile. Close to this spawning area, a new offshore kraft wood pulp mill effluent discharge system has been installed, raising considerable social concern regarding the fate of the anchoveta and sardine spawning area. Studies in Chile on the potential impact that industrial effluents might have on local pelagic species, are scarce. Accordingly, the aim of this study was to evaluate the direct effect of the kraft wood pulp secondary effluent on the early stages of the aforementioned species. In a first phase, using a reference toxicant, we validated and standardized the anchoveta embryos from the natural environment as a test organism for ecotoxicological evaluations considering egg mortality as the endpoint. In the second phase, utilizing the embryo tests, we assessed the effluent toxicity in a dilution series of salinity adjusted Kraft wood pulp secondary effluent using anchoveta and sardine eggs collected from the natural environment. During the late winter-early spring spawning seasons between 2007 and 2010 we carried out a series of short cruises to the coastal area off Talcahuano. The eggs collected from the field were separated from the plankton less than 2 h after collection and the early developmental stages (phase Ⅲ) were utilized in bioassays. Depending on the availability of eggs in the plankton, five eggs of each species were transferred to wells with freshly prepared test solutions and placed in temperature-controlled baths (12°C) under a 12 h light: 12 h dark photoperiod. The effluent stock solution salinity was set at 34 psu using hypersaline brine or synthetic sea water salt. Additionally, two extreme Potassium Dichromate concentrations (300 mgL-1 and 38.9 mgL-1) were included to check constancy in embryonic sensitivity. At hatching time (96 hrs), all rearing containers were checked and the number of dead embryos registered. The data were expressed as egg mortality and ANOVA was used to compare egg mortality between the effluent dilutions and controls. Our results from a series of seven bioassays performed with anchoveta embryos showed that three did not exhibit significant differences in the number of dead eggs between the effluent dilutions and controls (P＞0.05 mortality mean 13.7% ± 7.3). In the rest of the bioassays significant differences were only observed between the mortality in the control group (mean 22.1% ± 9.3) and the treatment with 100% effluent (mean 61.1% ± 27.8). These results indicate that embryos sensitivity to the effluent was variable among batches corresponding to different sampling dates, probably coincident with egg quality seasonal variability reported for anchoveta in this spawning area. With sardine embryos, four bioassays were mounted and the results indicated no differences in mortality between the control group (mean 5.6 % ± 4.2) and secondary effluent dilutions (mean 5.8% ± 10.4). Based on all the results obtained we concluded that: ⅰ) effluent dilutions present in the environment (＞1%) did not induce an increase in mortality of sardine and anchoveta embryos, ⅱ) only the 100% effluent treatment produced an increase in anchoveta embryo mortality and this was coincident with the period in which embryo quality decreases. This information highlights the importance of assessing the effluent effects in each species separately and also of the importance of taking into account the complete reproductive cycle.