Effect of nutrient conditions on the toxicity of naphthalene toChlorella pyrenoidosa

The toxicity of naphthalene to a freshwater microalga, Chlorella pyrenoidosa, and the subsequent recovery of algae from the damagewere investigated under two nutrient conditions, either enriched with nitrogen (N) and phosphorus (P), or starved of N and P. Resultsshowed that C. pyrenoidosa was more sensitive to naphthalene under N,P-enriched condition, and the inhibitory rate generally increasedat first and then decreased gradually with the evaporation of naphthalene under both nutrient conditions. Enriched N, P reduced theinhibitory rate at initial naphthalene concentration of 5 and 10 mg/L, but enhanced it at 100 mg/L, at which more severe ultrastructuredamages were found than those under N,P-starved condition. Observed damages included partly or totally disappearance of nucleolus,nuclear, and plasma membranes. According to the chlorophyll content and cell density measurements, C. pyrenoidosa could recoverfrom naphthalene damage with initial concentrations 6 50 mg/L in 7 days under both nutrient conditions, while they could not recoverif the initial concentration of naphthalene was at 100 mg/L. Under the N,P-starved condition, the inability of C. pyrenoidosa to recoverfrom the naphthalene damage was consistent with the results of high inhibitory rate, low value of specific growth rate (SGR, 0.05day??1), and the severe destruction of cell structure. However, under the N,P-enriched conditions, the observed lower inhibitory rate,higher value of SGR (0.55 day??1), and the intact cell structure of most cells suggested that algae could potentially recover from thenaphthalene damage.