|
Monocyclic aromatic hydrocarbons such as benzene, toluene, ethylbenzene andxylene （BTEX） are commonly used in the blending of petrol and also used as solventand raw material in chemical production such as paints, polymers andpharmaceuticals. As a consequence of their wide usage, they are common wastematerials. High levels of BTEX compounds in aquatic environment have often beendetected frequently, which led to serious effects to the aquatic systems and human. Inthis paper, toxicological effects of toluene, ethylbenzene and xylene on some typicalaquatic organisms were investigated, and we made an initial attempt to enact theWater Quality Criteria for BTEX （benzene, toluene, ethylbenzene and xylene）.Freshwater fish Misgurnus anguillicaudatus was adopted as experimental animalto study the acute and chronic toxic effects of toluene, ethylbenzene and xylene. Theacute toxicity test indicated that the96h-LC50of three pollutants were149.7,92.7and88.9mg/L, respectively. Exposed to toluene, ethylene and xylene at low level for14days, acetylcholinesterase （AChE）, lipid peroxidation, antioxidant defenses systemincluding superoxide dismutase （SOD）, peroxidase （POD）, catalase （CAT） andglutathione-S-transferase （GST） were studied. The result showed that physiologicalindicators tested differed in their sensitivities to different pollutants. Overall, AChEwas better to be a good indicator of ethylbenzene and xylene; antioxidant enzymeswere more suitable to indicate the toxicity of toluene and ethylbenzene, which GSTand POD were more suited to be biomarkers of oxidative stress of toluene andethylbenzene for a short time; GST was also sensitivity to the xylene for14days;MDA was more sensitive to the three pollutants. According to the date, theLowest-Observed-Effect Concentrations （LOECs） of toluene, ethylbenzene andxylene on Misgurnus anguillicaudatus were5,10and20mg/L, respectively.Macrophytes are playing a vital role in material circulation and energy flow inaquatic environment, however, the data were relatively limited and have served arelatively minor role in regulatory decision. Therefore, five macrophytes that widely distributed in China were chosen as experiment plants to study the toxic effects oftoluene, ethylbenzene and xylene. Chlorophyll contents, malondialdehyde （MDA）,superoxide dismutase （SOD）, peroxidase （POD） and catalase （CAT） in plants wereinvestigated. The result showed that the different physiology indexes in differentplants had various sensitivities to the three pollutants. Conclusion in general,biomarkers chosen in our research have worked well as indicators of toxic effects oftoluene, ethylbenzene and xylene in a short exposing time. The reason may be that theplants had been damaged due to prolonged exposing time; physiological indexes wereless sensitive than that at early exposure time to the pollutants. Another explanationwas that the macrophytes have gradually adapted to the stresses of pollutants, andthey could restore the metabolism functions to a certain degree.The results also indicated that the emergent aquatic plants was more resistance totoluene, ethylbenzene and xylene, and the submerged plants were more suitable toindicate the toxic effects. Comparing all the data based on toxicity test onmacrophytes, the Lowest-Observed-Effect Concentrations （LOECs） of toluene onHydrilla verticillata, Vallisneria spiralis, Oenanthe javanica （Blume） DC and SpikedLoosestrlfe were7.30,5.00,10.00and5.00mg/L, respectively; LOECs ofethylbenzene on the four plants were1.15,5.00,5.00and5.00mg/L, respectively；LOECs of xylene on the four plants were2.36,5.00,5.00and5.00mg/L,respectively.In order to derive Water Quality Criteria that can protect the freshwaterecosystem and biota system, all available toxicity data of BETX to Chineserepresentative species in freshwater were collected. Three widely used criteriaderivation methods including the toxicity percentile rank method, species sensitivitydistribution and assessment factor method were used to derive aquatic life criteria forthe three substances. The results showed that for toxicity percentile rank method，thecriteria maximum concentrations of benzene, toluene, ethylbenzene and xylene were2.34,6.73,2.54and5.36mg/L respectively，the criteria continuous concentrationswere NA,0.49,0.27and0.72mg/L respectively; for species sensitivity distributionmethod，the criteria of short term hazardous concentrations of four substances were 9.77,8.55,5.87and10.39mg/L, the long term hazardous concentrations were NA,0.62,0.63and1.42mg/L，respectively; for the assessment factor method，the criteriaof freshwater benzene, toluene, ethylbenzene and xylene were expressed by one value，which were0.58,0.46,0.11and0.15mg/L for toluene, ethylbenzene and xylene.Meanwhile，the criteria values for freshwater were studied and compared among thethree methods. It showed that the toxicity percentile rank method was more suitablethan the other two methods to derive Water Quality Criteria in our study. The criteriavalues derived from the toxicity percentile rank method can protect a wider range ofaquatic organisms.Based on all the analysis, the final recommended Water Quality Criteria forBTEX （benzene, toluene, ethylbenzene and xylene） in freshwater were that thecriteria maximum concentrations of benzene, toluene, ethylbenzene and xylene were2.34,6.73,2.54and5.36mg/L respectively，the criteria continuous concentrationwere NA,0.49,0.27and0.72mg/L. We couldn’t derive the criteria of chronictoxicity for benzene for lack of the chronic toxicity values, so it remains to beimproved in future research.
|