The Toxicity And Mechanism Of Naphthalene And Phenanthrene To Chlorella Sp. Under Different Nutrient Conditions

Eutrophication could not only cause red tide and water bloom pollution, affecting the ecosystem and application of water bodies, but also affect the toxicity of pollutants. PAHs were a serious of persistent organic pollutants being ubiquitous in water. To study the effect of eutrophication on the toxicity of PAHs may give some references in setting the concentration criteria for the water quality standard in future.For their widely distributing in water body, Chlorella pyrenoidosa and Chlorella vulgaris were selected as target organism to study the toxicity of naphthalene and phenanthrene under different nutrient conditions, and relevant mechanism was discussed in this study. Some useful information was listed below:(1) The toxicity of naphthalene to freshwater C. pyrenoidosa and marine C. vulgaris under different nutrient conditions (N,P-enriched and N,P-starved condition) were studied in open system. For C. vulgaris, naphthalene inhibited the growth in all treated groups, and enriched medium enhanced the inhibitory rate. For C. pyrenoidosa, enriched N,P reduced the inhibitory rate at lower naphthalene initial concentration of 5 and 10 mg/L, but enhanced it at the higher concentration of 100 mg/L, at which more severe untrastructural damages were found than those under N,P-starved condition, involving partly or totally disappearance of nucleolus, nuclear and plasma membrane. MDA and chlorophyll contents showed that naphthalene was more toxicity in N,P-enriched condition compared to N,P-starved condition.(2) The toxicity of naphthalene and phenanthrene to freshwater C. pyrenoidosa under different condition of carbon resource (2 g/L NaHCO3 and glucose with same TC content) were studied in sealed system. Naphthalene and phenanthrene enhanced the inhibitory rate of C. pyrenoidosa in inorganic carbon (IC)-enriched medium compared to those in organic carbon (OC)-enriched medium. Supplement of OC enhanced the growth, chlorophyll content and chlorophyll a:b of C. pyrenoidosa compared to supplement of IC. Cell wall became thicker in IC-enriched medium, while starches increased obviously in OC-enriched medium. Naphthalene and phenanthrene both enhanced the accumulation of starches. Ultra-structure of C. pyrenoidosa showed that algal cells were destroyed more seriously in OC-enriched medium.20 mg/L naphthalene killed C. pyrenoidosa in OC-enriched medium while it didn't in IC-enriched medium.1.2 mg/L phenanthrene did not kill the algae in both IC and OC-enriched medium.