Toxic effects of some major polyaromatic hydrocarbons found in crude oil and aquatic sediments on Scenedesmus subspicatus.

The green alga, Scenedesmus subspicatus was exposed for 7 days to a series of PAHs (polyaromatic hydrocarbons) of increased molecular weight from two to five rings [naphthalene (Nap), anthracene (Ant), phenanthrene (Phe), pyrene (Pyr) and benzo(a)pyrene (BaP)]. The toxicity measured as population growth inhibition by individual PAH to the S. subspicatus followed the order: BaP>Pyr>Ant>Phe>Nap. These results confirmed that the toxicity potential of PAHs seems to be strongly influenced by their physico-chemical properties (aqueous solubility, K(ow), coefficient of volatilization, etc.) and the conditions of algae culture (light, presence of nitrate ions, etc.). Consequently, Nap, Phe and Ant having low k(ow) values and low coefficient of volatilization values were less toxic than BaP with the highest k(ow) value, indicating for example why Nap with the lowest EC(50) value was nearly 2 x 10(5) times lower than that of BaP. Moreover, nitrate ions seemed to act directly on the degree of hydroxylated radical reactivity of PAHs, since BaP always remained the most toxic of the compounds tested. The results were also agreed with the QSAR model for toxicity prediction of PAHs to many aquatic organisms.

Freshwater microcosms-based assessment of eco-toxicological effects of a chemical effluent from the Pilcam industry in Cameroon.

We studied the acute toxicity of a raw effluent from a battery manufacturing plant (Pilcam) in Douala, Cameroon, to a freshwater fish (Oreochromis niloticus), and subsequently evaluated its sub-acute effects on water quality and the biota in freshwater microscosms. The acute toxicity test was based on 96 hrs static renewal bioassays that resulted in 96-h LC50 and LC90 values of 16 and 20.7% (v/v), respectively. The sub-acute experiments were conducted by exposing several species of aquatic organisms (plankton, macroinvertebrates and mollusks) to lower effluent concentrations [1.6%, 8.0%, 16% (v/v)] for six weeks, and monitoring their survival rates, as well as the physical and chemical characteristics of water. These concentrations were based on 10%, 50%, and 100% of the 96 h - median lethal concentrations (LC50) of the effluent to the freshwater fish, Oreochromis niloticus. Significant effects on functional parameters, such as, chlorophyll-a and total protein could not be demonstrated. However, the activity of alkaline phosphatase was significantly inhibited at all concentrations tested. Phytoplankton, zooplankton, macro-invertebrate communities and snails were negatively affected by the effluent application at concentrations ? 8% (v/v), with chlorophyta, ciliates, ostracoda, annelida, planaria and snails being the most sensitive groups. The snails were eliminated after 24 h exposure from microcosms treated with effluent at concentration ? 8% (v/v). Effluent exposure also caused significant effects on water quality parameters (DO, pH, hardness, conductivity, color, turbidity, ammonia) in general at concentrations ? 8% (v/v). Temperature and alkalinity were not significantly affected. Overall, data from this research indicate that a dilution of the Pilcam effluent down to 1.6% does not provide protection against chronic toxicity to aquatic organisms. Further studies are needed to determine the no observable adverse effect level (NOAEL), as well as a chronic reference concentration for this effluent.

[Evaluation of bacterial and polluting loads of effluent from activated sludge wastewater treatment plants in Yaounde, Cameroon]. / Evaluation de la charge polluante et de la charge bactérienne des rejets des stations d'épuration a boues activées Yaoundé (Cameroun).

Activated sludge wastewater treatment plants in Yaounde are plagued by failures in their operation. A microbiological and physico-chemical study was carried out on wastewater effluent of an hospital, university campus, and two residential areas made up of more than 2,000 apartments connected to two collective sewase systems. Wastewater sampling was performed in the form of daily cycles during which composite samples were made every two hours with samples collected every half hour. Variables measured included incoming flow rates, suspended solids, pH, electrical conductivity, ammonia nitrogen, total Kjeldahl nitrogen (combination of ammonia and organic nitrogen) and total reactive phosphorus, BOD5 and COD. Microorganisms were isolated on selective culture media using membrane filter procedures. The results obtained show that effluent discharged in receiving waters are, in general, not treated. The suspended solids contents of raw sewage range from 120 to 2,600 mg/l. In General Hospital a mean value of suspended solids of 31.8 mg/l was obtained for treated wastewater. pH values of both raw and treated sewage range from 6 to 8.5 units. Mean values of the conductivity of treated and raw wastewater range from 449.7 to 1,038.3 microseconds/cm. The TKN contents of untreated wastewater are comprised between 36 and 259.2 mg/l. These values range from 5 to 20 mg/l for treated effluent in the General Hospital plant. Large amounts of total hydrolysable phosphorus varying from 3.8 to 27.9 mg/l are present in wastewater from the plants. Influent BOD5 of Grand Messa, Cite Verte and university campus wastewater range from 110 to 530 mgO2/l. Values recorded indicate an important input of organic matter to receiving waters. In the case of biotic components, test germs densities registered in the influent of Grand Messa and those of Cite Verte are comprised between 9 x 106 and 88 x 107 CFU/100 ml for fecal coliforms, and between 9 x 105 and 74 x 107 CFU/100 ml for fecal streptococci. The densities of Aeromonas hydrophila in Grand Messa and Cite Verte influent fluctuate between 30 x 106 and 65 x 108 CFU/100 ml. Influent of university campus harbour 10 x 105. Densities of Pseudomonas aeruginosa remain below 70 x 105 CFU/100 ml. Treated effluent BOD5 values range from 48 to 150 mgO2/l. Such values indicate an inefficient treatment. The decrease in bacterial densities is limited to 2 logarithmic units. Treated effluent still harbour 10 x 103 to 10 x 105 CFU/100 ml for fecal coliforms, and 20 x 102 to 12 x 104 CFU/100 ml for fecal streptococci. These values range from 10 x 104 to 50 x 105 CFU/100 ml for Aeromonas hydrophila. Pseudomonas aeruginosa densities remain in general below 40 x 104 CFU/100 ml. Discharges from these wastewater treatment plants are responsible for the permanent fecal contamination of the environment and a lack of proper hygiene. Furthermore, they produce overfertilization of receiving waters.

[Bacteriological quality of spring and well water in Yaounde (Cameroon)]. / Qualité bactériologique des eaux des sources et des puits de Yaoundé (Cameroun).

The drinking water supply in Yaounde, Cameroon, often fails to meet demand and this leads many people to seek water from springs and wells the microbiological quality of which is unknown. We carried out a microbiological survey of five spring water points and ten wells. The fifteen study sites were located in various residential districts and were selected according to geographical location and number of users. Microorganisms were isolated on specific culture media using the membrane filter technique. We found that these water supplies contained many types of bacteria including Pseudomonas aeruginosa, Aeromonas hydrophila and indicators of fecal contamination. Maximum annual concentrations differed at the various sites and over time, from 750 to 98,000 CFU/l for P. aeruginosa, 40 to 78,000 CFU/l for A. hydrophila and 300 to 58,000 CFU/l for fecal indicator bacteria. The density of fecal bacteria was strongly correlated (p < 0.01) with those of P. aeruginosa in spring water and A. hydrophila in well water. The degree of correlation between microbial concentrations differed between sites. The source of fecal contamination differed between sites and was animal, human or both. The densities of bacteria recorded were high. Therefore, consumers of water drawn from these sources are at short-term risk of contracting waterborne diseases.

The urgent need for environmental sanitation and a safe drinking water supply in Mbandjock, Cameroon.

Studies were conducted to assess the physical, chemical, and bacteriological qualities of drinking water in Mbandjock, Cameroon. Study results indicated that the vast majority of drinking water sources possessed acceptable physical and chemical qualities, according to the World Health Organization standards. However, microbiological analyses revealed that only the waters treated by the Cameroon National Water Company (SNEC) and the Sugar Processing Company (SOSUCAM) were acceptable for human consumption. All spring and well waters presented evidences of fecal contamination from human and/or animal origin. Water from these sources should, therefore, be treated before use for drinking. Since the majority of the population gets its water from wells and springs, there is an urgent need to develop a health education program, within the framework of primary health care, with respect to environmental sanitation and safe drinking water supply in this community.

Field tests of a village-based mollusciciding programme for the control of snail hosts of human schistosomes in Cameroon.

The feasibility of using unskilled workers at the district or village level to perform mollusciciding activities in arid regions of northern Cameroon was investigated. A simplified procedure for application to temporary ponds, the principal sites of schistosomiasis transmission in that region, was tested. This consisted of mixing the required quantity of niclosamide (Bayluscide, Bayer AG, Leverkusen) with pond water in a plastic watering can and applying the mixture around the circumference. To aid dispersion, the can was repeatedly swept from the perimeter toward the centre of the pond. Two ponds each were treated once near the end of the rainy season at 1 of 3 concentrations: 0.5, 1.0 and 1.5 p.p.m. Following treatment, 100% snail mortality was recorded at all concentrations. A simple, rapid method for determining the quantity of niclosamide needed to treat temporary ponds was also devised. Physical characteristics were determined for 16 potential schistosomiasis transmission sites in the region. An integration of those characteristics was used to develop a simplified scale indicating the quantity of niclosamide needed to treat ponds based on their circumference. The operational feasibility of a village based mollusciciding programme using those simplified procedures was then evaluated in 2 villages. Village health workers demonstrated a high accuracy (87%) in identifying potential schistosomiasis transmission foci and snail host populations were virtually eliminated from treated sites.

Geographical variation of the potency of the plant molluscicide phytolacca dodecandra (Endod) to two Species of aquatic snails in Uganda

This study is aimed at assessing the geographical variation of the potency of the African soap berry plant Phytolacca Dodecandra; in Uganda and of Endod (its Ethiopian name); to the schistosomiasis -transmitting snail Biomphalaria sp. and Bulinus sp

A new method for determining concentrations of Endod-S (Phytolacca dodecandra) in water during mollusciciding.

A hemolytic method was developed for the quantitative determination of oleanane saponin (Endod-S) in Phytolacca dodecandra (Phytolaccaceae), a plant with potent molluscicidal properties. A chemical method based on thin-layer chromatography (TLC) was used as a control for comparison with a hemolysis test. Standard curves for calibration of both tests of Endod-S gave high correlation coefficients. The hemolysis method gave a correlation coefficient of 0.98 for saponin (Endod-S) levels ranging from 1.6 to 4.2 mg/l. The TLC method gave a correlation coefficient of 0.99 for saponin levels above 1.5 micrograms. Due to the action of saponins on erythrocytes, the hemolysis method could not be used at levels below 1.6 and above 4.2 mg/l. Similarly, sample size limited TLC quantitation of these saponins at levels below 1 microgram. Both the TLC and the hemolysis methods on identical Endod-S water samples gave comparable results at saponin levels between 2 and 6 mg/l. A snail bioassay showed that the LC50 and the LC90 concentrations of Endod-S to the snail Biomphalaria glabrata (albino) were 2.57 and 2.92 mg/l respectively. These values fell in the standard curve range for the hemolysis method thus indicating that the hemolysis method is of practical value for testing Endod-S concentrations that would actually be used in field applications for snail control. The hemolysis method is less expensive than TLC and can be easily adapted to field conditions.

Interpretation of microbial bioassays using kinetic parameters.

A method analogous to that used for enzyme kinetics was applied to estimate maximum growth rates and oxygen depletion rates as measures of microbial toxicity. Selected toxicants including phenol, formalin and CuSO4 were tested against an axenic culture of E. coli and a mixed culture derived from soil to determine reproducibility of the test procedures. Optical density was used as a measure of growth over time. Oxygen uptake over a short term (less than 20 min.) and over extended time (greater than 4 hrs.) was also monitored. Microbial growth rate constants (g) and oxygen depletion rate constants (k) were calculated and the EC50 values for toxicity were taken as one half the maximum growth rate or oxygen depletion rates, respectively. The method proved a reasonable and reliable measure of toxicity.