Plant-enhanced phenanthrene and pyrene biodegradation in acidic soil.

A study was undertaken to assess if corn plant (Zea may L.) may be able to enhance the degradation of phenanthrene and pyrene in acidic soil inoculated with a bacterial strain (Pseudomonas putida MUB1) capable of degrading polycyclic aromatic hydrocarbons (PAHs). Planting with corn, inoculating with MUB1, or a combination of the two were found to promote the degradation of phenanthrene and pyrene in acidic soil at different rates. In the presence of corn plants, the rates of phenanthrene and pyrene removal were 41.7 and 38.8% in the first 10 days, while the rates were 58.8 and 53.6%, respectively, in the treatment which received MUB1 only. After 60 days, the corn + MUB1 treatment led to the greatest reduction in both phenanthrene and pyrene biodegradation (89 and 88.2%, respectively). In control autoclaved soil, the rates of phenanthrene and pyrene removal were 14.2 and 28.7%, respectively, while in non-autoclaved soil, the rates were 68.7 and 53.2%, respectively. These results show that corn, which was previously shown to grow well in PAH-contaminated acidic soil, also can enhance PAH degradation in such soil. Inoculation with a known PAH degrader further enhanced PAH degradation in the presence of corn.

Histopathological alterations of Nile tilapia, Oreochromis niloticus in acute and subchronic alachlor exposure.

Histopathological alterations in Nile tilapia, Oreochromis niloticus, aged 3 months and subjected to acute and subchronic alachlor exposure were studied by light microscopy LC50 values of alachlor for 24 hr 48 hr, 72 hr and 96 hr were 963.6, 563, 448, and 381.9 microg l(-1), respectively and the maximum acceptable toxicant concentration (MATC) was 350 microg l(-1). Fish were exposed to 381.9 (acute) and 35 microg l(-1) (sub-chronic) of alachlor for 24, 48, 72 and 96 hr and 90 days, respectively Gill lamellae and kidney tubules were the primary target organs for the acute toxic effect of alachlor while in the subchronic exposure, the toxic effect on the gills was less marked than that of the kidneys and liver Gill alterations included edema of the epithelial cell system, aneurisms with some ruptures, hypertrophy and hyperplasia of epithelial cells. The liver showed hydropic swelling of hepatocytes and vacuolation. Lipid vacuoles were observed in hepatocytes in the second and third month of subchronic exposure. The kidney showed hydropic swelling of tubular cells, lipid vacuole accumulation in many tubules, and nuclear pyknosis. The findings of this study could be used as a guideline forbiomonitoring programs on populations of Nile tilapia cultured near alachlor contaminated areas.

Toxicity and bioaccumulation of cadmium and lead in Salvinia cucullata.

The toxicity and accumulation of heavy metals, cadmium (Cd) and lead (Pb) in aquatic fern, Salvinia cucullata were studied. Plants were cultured in Hoagland's medium which was supplemented with 0.5,1,2, and 4 mg/l of Cd and 5, 10, and 40 mg/l of Pb and were separately harvested after 2,4,6, and 8 days. The toxicity symptoms of Cd and Pb to S. cucullata showed chlorosis on leaves. There were significant derceases in the relative growth, biomass productivity and total chlorophyll content when the exposure time and concentration were increased. The accumulation study showed the significant increases of both metals when the exposure time and concentration were increased. The roots of S. cucullata had higher Cd and Pb contents than leaves suggesting that the metals were bound to the root cells and were partially transported to the leaves.

Toxicity and accumulation of lead and chromium in Hydrocotyle umbellata.

The aquatic plant, Hydrocotyle umbellata, was studied for its toxicity and accumulation of lead (Pb) and chromium (Cr) in a synthetic solution. Plants were cultured in a modified Hoagland's nutrient solutions supplemented with 20, 40, 60, 80, and 100 mg Pb/l as lead nitrate [Pb(NO3)2] and 2, 4, 6, 8, and 10 mg Cr/l as potassium dichromate (K2Cr2O7). They were separately harvested after 3, 6, 9, and 12 days. Plants exposed to Pb and Cr showed significant decreases in the biomass productivity and total chlorophyll content when the exposure time and metal concentration were increased. The accumulation of Pb and Cr in the plants was significantly increased, but it was not linear with the exposure time and metal concentration. Both metals were accumulated higher in the roots than in the shoots. The bioconcentration factor of Pb was higher than that of Cr at the same exposure time, indicating a higher accumulation potential of Pb than Cr in H. umbellata. Toxicity symptoms of both metals showed a reduction in the production of new plantlets, withering of petioles, and change in color of roots from light green to dark brown. Pb caused leaf chlorosis, whereas Cr caused leaf necrosis. The toxicity symptoms increased when the exposure time and metal concentration were increased.