Wet weather impact on trihalomethane formation potential in tributaries to drinking water reservoirs

During rain storm events, land surface runoff and resuspension of bottom sediments cause an increase in Trihalomethane (THM) precursors in rivers. These precursors, when chlorinated at water treatment facilities will lead to the formation of THMs and hence impact drinking water resources. In order to evaluate the wet weather impact on the potential formation of THMs, river samples were collected before, during and after three rain storms ranging from 15.2 to 24.9 mm precipitation. The samples were tested for THM formation potential and other indicators including UV254 absorbance, turbidity and volatile suspended solid (VSS). Average levels of THMs increased from 61 μg/l during dry weather to 131 μg/l during wet weather, and then went back to 81 μg/l after rain ended. Wet weather values of THM are well above the maximum contaminant level (MCL) 80 μg/l, set by EPA for drinking water. THM indicators also exhibited similar trends. Average levels increased from 0.6 to 1.8 abs; 2.6 to 6 ntu; and 7.5 to 15 mg/l respectively for UV254, turbidity and VSS. A positive correlation was observed between THM formation and THM indicators. The t-test of significance (p-value) was less than 0.05 for all indicators, and R values ranged from 0.85 to 0.92 between THMs and the indicators, and 0.72 to 0.9 among indicators themselves.     

Monitoring the Trihalomethanes Present in Water After Treatment with Chlorine Under Laboratory Condition

In this work assays involving chlorinated water samples, which were previous spiked with humic substances or algae blue green and following the production of the THMs for 30 days is described. To implement the assays, five portions of 1,000 ml of water were stored in glass bottles. The water samples were treated with solutions containing 2, 3, 4 and 5 mg l⁻¹ chlorine. The samples aliquots (60 ml) were transferred into the glass vials, 10 ml were removed to have a headspace and 100 μl of the 10 mg l⁻¹ pentafluortoluene bromide solution was added to each vial. The extraction step was performed by adding 10 g of Na₂SO₄ followed by 5 ml of n-pentane. The vials were stopped with a TFE-faced septum and sealed with aluminum caps. The generated THMs were determined by gas chromatography with electron capture detector using reference solutions with concentration ranging from 8 to 120 μg l⁻¹ THMs. Three assays were monitored during 30 days and chloroform was the predominant compound found in the water samples, while other species of THMs were not detected. The results showed that when the chlorine concentration was increased in water samples containing algae the concentration of THM varied randomly. Nevertheless, in water samples containing humic substances the increase of the THM concentration presented a relationship with the chlorine concentration. It was also observed that chloroform concentration increased with the elapsed time up to one and six days to water samples spiked with humic substances and algae blue green, respectively and decreased along 30 days. By other hand, assays performed using water samples containing decanted algae material showed that THM was not generated by the chlorine addition.     

Comprehensive screening and priority ranking of volatile organic compounds in Daliao River,China

An analytical strategy for comprehensive screening of target and non-target volatile organic compounds (VOCs) in surface water was developed, and it was applied to the analysis of VOCs in water samples from Daliao River. The target VOCs were quantified using purge and trap-gas chromatography-mass spectrometry (P&T-GC/MS). Among 20 water samples, 34 VOCs were detected at least once. For the screening of non-target VOCs, the double distillation apparatus was used for the pre-concentration of VOCs prior to P&T-GC/MS analysis. Subsequently, deconvolution software and NIST mass spectral library were applied for the identification of the non-target compounds. A total of 17 non-target VOCs were identified. The most frequently detected VOCs (detection frequencies >80 %) included toluene, benzene, naphthalene, 1,2-dichloroethane, 1,1,2-trichloroethane, and methyl tert-butyl ether. The distribution of VOCs obviously varied according to the sampling sites. The total concentrations of VOCs in water samples collected from the heavily industrialized cities (Anshan and Liaoyang) and the busy port city (Yingkou) were relatively high. The top ten priority VOCs, including naphthalene, 1,2-dichloroethane, o-xylene, 1,3-dichlorobenzene, tetrachloroethene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, ethylbenzene, m-xylene, and p-xylene, were obtained by the ranking of the detected VOCs according to their occurrence and ecological effects. These compounds should be given more attention in monitoring and drainage control strategies.     

中国沿海三省主要饮用水源有机物监测

采用固相萃取、吹扫捕集和气相色谱-质谱联用仪(GC-MS)对江苏、浙江、山东省的21个主要地表饮用水源、126份水样中的25种VOCs、38种SVOCs进行定量检测。结果有19种VOCs、10种SVOCs至少在一个水源地多次被检出,其中挥发性氯代烃、苯系物、氯代苯类、酚类、硝基苯类、酞酸酯类、农药为中国或美国环境保护局提出的"水中优先控制污染物",最高检出量为27.79μg/L。三省主要地表水受到有机物轻度污染,水体中VOCs、SVOCs含量尚未超过《地表水环境质量标准》(GB 3838-2002)和《生活饮用水卫生标准》(GB 5749-2006)限值,工业废水排放及农田雨水径流是地表水有机物的重要来源。     

Multivariate statistical study of seasonal variation of BTEX in the surface water of Savitri River

Volatile organic compounds (VOCs) analysis was carried out for the surface water of the Savitri river during the period of June 2005 to June 2007. BTEX compounds (Benzene, Toluene, Xylene & Ethyl benzene) were analyzed by using micro extraction technique (Purge & Trap). Concentrations of these BTEX compounds were ranging from 0.1 to 1.5 ppm during sampling period. Higher concentrations of BTEX were found at sampling location VI. Concentration of ethyl benzene was very low as compare to other compounds. However, the concentration of benzene was very high. Seasonal variations in conc. of BTEX compounds were observed and higher concentration was detected during the summer season. Salting-out effect had given higher quantification values. In PCA and PFA, the component loading for all the variables are positively correlated. Death of fishes was observed in the river that is indication of severe pollution problem.     

Iron content in groundwaters of Visakhapatnam environs, Andhra Pradesh, India

Trace elements are essential for human health. However, excess concentrations of these elements cause health disorders. A study has been carried out in Visakhapatnam environs, Andhra Pradesh, India to ascertain the causes for the origin and distribution of iron content in the groundwaters. Fifty groundwater samples are collected and analyzed for iron. The content of iron ranges from 400 to 780 μg/l. A comparison of groundwater data with rock and soil chemistry suggests that the concentration of iron (400–530 μg/l) in the groundwaters is derived from the rocks and soils due to geogenic processes. This concentration is taken as a natural occurrence of iron in the groundwaters of the study area for assessing the causes for its next higher content (>530 μg/l). Relatively higher concentration of iron (540–550 μg/l) is observed at some well waters, where the wells are located nearby municipal wastewaters, while the very high concentration of iron (610–780 μg/l) is observed in the industrially polluted groundwater zones, indicating the impact of anthropogenic activities on the groundwater system. These activities mask the concentration of iron caused by geogenic origin. Hence, both the geogenic and anthropogenic activities degrade the groundwater quality. Drinking water standards indicate that the iron content in all the groundwater samples exceeds the permissible limit (300 μg/l) recommended for drinking purpose, causing the health disorders. Necessity of close monitoring of groundwater quality for assessing the impact of geogenic and anthropogenic sources with reference to land use/land cover activities is emphasized in the present study area to protect the groundwater resources from the pollution.     

Water quality assessment: surface water sources used for drinking and irrigation in Zaria,Nigeria are a public health hazard

We assessed the quality and pollution status of source surface waters in Zaria, Nigeria by monitoring the nature, cause and extent of pollution in Samaru stream, Kubanni River and Kubanni dam over a period of 10 months, between March and December 2002. A total of 228 water samples was collected from 12 sites and analysed for a total of ten physicochemical and one bacteriological quality indicators, using standard methods. Aesthetic water quality impairment parameters were also observed. The mean values of most water quality parameters were significantly higher (P < 0.05) in both the stream and river than in the dam. There was no significant correlation between faecal coliform counts (FCC) and water temperature (in the range 15–33°C); pH (5.77–7.32); and turbidity (1.4–567 NTU). The high FCC ranged from 2.0 × 10¹ to 1.6 × 10⁶ MPN/100 ml and exceeded the WHO standards for drinking water and water used for fresh-produce irrigation, and correlated positively (P < 0.05) with conductivity (in the range 68–1,029 μS/cm); TDS (10.0–70.0 mg/l); TSS (10.0–70.0 mg/l); Cl (7.5–181 mg/l); PO₄⁻P (0.01–0.41 mg/l); NO₃⁻N (0.6–3.8 mg/l) and BOD₅ (0.1–14.9 mg/l). The main pollution sources were municipal wastewater, stormwater runoffs, the ABU sewage treatment plant, abattoir effluents and irrigation farms treated with chemical fertilisers. We conclude that these water bodies are potentially hazardous to public health and that proper sewage treatment and river quality monitoring are needed to warn against hazards to public health.     

吹扫—捕集／气相色谱法测定水中挥发性有机物

为提高样品分析效率,研究并建立了吹扫-捕集／气相色谱／氢火焰检测器联用同时测定水中1,2-二氯乙烷、苯、甲苯、氯苯、乙苯、对-二甲苯、间-二甲苯、苯乙烯、邻-二甲苯、异丙苯、1,4-二氯苯、1,2-二氯苯、硝基苯、1,3,5-三氯苯、1,2,4-三氯苯、1,2,3-三氯苯、六氯丁二烯17种挥发性有机物的分析方法。结果表明,当进样体积为25．0ml时,最低检出限为0．0034-0．1088μg/L,相对标准偏差为1．8％～6．4％,加标平均回收率为97．6％-105．8％。该方法可快速、简便、准确、高灵敏度的测定水中17种挥发性有机物,并适用于饮用水和地表水中挥发性有机物的测定。     

Risk Assessment of Organic Pesticides Pollution in Surface Water of Hangzhou

Advances in research on pollution of organic pesticides (OPs) in surface water, pollution survey and risk assessments of organochlorine pesticides (OCPs) and organophosphorus pesticides (OPPs) of surface water in Hangzhou are conducted. Total concentrations of dichloro-diphenyl-trichloroethane (DDT) and hexachloride-benzene (HCH) in surface water were observed to be 0–0.270 μg/L and 0–0.00625 μg/L respectively. DDE, as a metabolite of DDT and many species of OPP_S were determined in some samples of surface water. Parathion, the main pollutant among OPPs in surface water of Hangzhou, was observed to be 0–0.445 μg/L. Based on these experimental results, health risk assessments on the organic pollution are developed. It is observed that the total risk “R ^T” at present time of surface water in Hangzhou is mainly contributed by organophosphorus pesticides, especially Parathion; HCH and DDT are not the main contaminants; on the contrary, organophosphorous pesticides, especially Parathion, must be of concern at the present time.     

Trihalomethane formation potential in treated water supplies in urban metro city

Trihalomethane (THM) formation potential (TFP) is very useful test to assess the level of the formation of trihalomethanes in worst case scenario. Organics in water have the potential to generate harmful disinfection by-products (DBPs) such as THMs, as a result of their reaction with disinfectant chlorine used in drinking water. DBPs are increasingly recognized as cancerous agents. TFP of postchlorinated treated water were investigated at six water treatment plants (WTPs) in Delhi City (India). The present paper presents the current trends of TFP so that prevention and control measures can be initiated by the regulating agencies responsible for drinking water supply. Liquid–liquid extraction method, followed by qualitative and quantitative estimation by gas chromatograph equipped with electron capture detector, had been used for the determination of THMs in water samples collected at the outlet just before supplying to the consumers during 2000–2007. The TFP values from 2004 onward of all WTPs did not exceed the WHO guideline value of ≤1.     

Hydrogen Peroxide and Ultraviolet Irradiations in Water Treatment

Trihalomethanes (THMs) the by-products of chlorination in water treatment are recognised as a threat to public health due to their carcinogenicity. The photodegradation of THMs using hydrogen peroxide has been found to give increased removal efficiency and the outcome of the study may find, its application in designing a unit process for water treatment. Batch experiments were carried out using UV lamp of 83 W and 40% w/w Hydrogen peroxide (H₂O₂) in test waters between 2.5–10 pH range of chloroform, bromodichloromethane, dibromochloromethane and bromoform at 50–200 μg L⁻¹ initial concentration. 92–100% removal of chloroform, bromodichloromethane, dibromochloromethane and bromoform were found with 0.1% of H₂O₂ and 90 min of UV exposure.     

Monitoring of Coliforms and chlorine residual in water distribution network of Rawalpindi, Pakistan

The present study was undertaken to examine the drinking water quality of Rawal Treatment Plant, Rawalpindi and its distribution network by collecting samples from eight different locations. The aim was to determine potential relationship between the presence of microorganisms and chlorine residual in the distribution network. Quantification of chlorine residual, turbidity, standard plate count (SPC), fecal and total coliforms by Most Probable Number (MPN) was performed. Three different forms of chlorine were measured at each sampling station such as free chlorine, residual chlorine, chloramines and total chlorine residual. A critical evaluation of data presented indicated that pH generally ranged from 7.02–7.30; turbidity varied from 0.34–2.79 NTU; conductivity fluctuated from 359–374 μS/cm; and TDS values were found to be ranging between 180–187 mg/l. Station # 7 was found to be most contaminated. The value of total chlorine was found to be 0.86 to1.7 mg/l at Station # 3 and 6, respectively. Highest standard plate count was 62 CFU/ml at Station # 7. Total coliforms were less than 1.1 MPN/100 ml at almost most of the stations except at Station # 3 where it was found to be greater than 23.0 MPN /100 ml. Overall aim of this study is to create awareness about contamination of drinking water in the water distribution networks and to make recommendations to provincial agencies such as EPA, CDA and WASA that regular monitoring should be carried out to ensure that the chlorine residual is available at consumer end.     

Arsenic and Other Metal Contamination of Groundwaters in the Industrial Area of Thessaloniki, Northern Greece

In groundwater, used for drinking water supply in the greater industrial area of Thessaloniki, in Northern Greece, concentrations of total arsenic exceeded the WHO provisional guideline value and the EU maximum contaminant level (MCL) of 10 μg/L. The concentration of total arsenic was in the range between 4–130 μg/L, whereas the median value was 36 μg/L and the average concentration 46 μg/L. Nine out of the eleven wells contained total arsenic at concentration higher than 10 μg/L and it should be stressed that 6 of them contain arsenic at concentrations between 10 (new MCL) and 50 μg/L (previous MCL). The examined groundwaters were found to contain elevated concentrations of manganese and phosphate. Arsenic had a positive correlation with the pH, indicating the possible effect of pH on arsenic mobilisation. These findings emerge the problem of contamination from arsenic, since, according to the EU directive 98/83, all drinking water sources within the European Union should have achieved compliance with the new limits by 12/2003, implying that the situation requires urgent remedial action.     

Effects of Cadmium (CdCl2) on development and hatching of eggs in European squid (Loligo vulgaris Lamarck, 1798) (Cephalopoda: Loliginidae)

This is the first study related to the effects of cadmium (Cd) on the development and hatching of eggs of Loligo vulgaris. The eggs were exposed to concentrations varying from 10 to 100,000 μg Cd/l for up to 1 month. During the study period natural sea water salinity (37 PSU), ambient temperature (ranging 16.5–21.5°C) and light conditions of 12-h light: 12-h dark for 744-h were used prior to the hatching. For 96-h, mortality rate of 100% of the eggs was found at cadmium concentration of 100,000 μg Cd/l, and the same mortality rate of the eggs were found at 1,000 and 10,000 μg Cd/l for 744-h and 696-h, respectively. Hatching took place between hours 456 and 576 in the control group and between hours 480 and 576 in 10 and 100 μg Cd/l groups. Total hatching rates were calculated to be 98.2 ± 1.6% for control group, 99.4 ± 0.6% for 10 μg Cd/l group and 98.6 ± 1.2% for 100 μg Cd/l group. Hatching successes were estimated as 69.5 ± 13.8% for control group, 84.5 ± 8.2% for 10 μg Cd/l group and 76.9 ± 5.9% for 100 μg Cd/l group. In the 100,000 μg Cd/l treatment, the egg degeneration began from animal pole of the eggs in 16 h, and 50% and 100% of them died in the initial stage at 72-h and 96-h, respectively. In the 10,000 μg Cd/l group, the eggs which reached at stage 19 (IX) were deformed and 50% and 100% of them died at 312-h and 696-h, respectively. In 1,000 μg Cd/l group, however, the eggs developed abnormally from stage 21 (X–XI) and reached at stage 29 (XIX), and 50% and 100% of them died in 624-h and in 744-h, respectively. There were significant differences in survival rates of the eggs among the concentrations (p < 0.05). The current study demonstrated that Cd adversely affects the development, survival and hatching of L. vulgaris eggs; however, no mortality was observed in 10 μg Cd/l and 100 μg Cd/l groups.     

Survey of Levels of Phthalate Ester Plasticizers in a Sewage Lagoon Effluent and a Receiving Stream

In this study, samples from a sewage treatment lagoon and those from a receiving stream were analyzed for their phthalate esters content. Knowledge of the distribution of ubiquitous phthalate esters in the sewage lagoon and the receiving stream was necessary because of the reports of their subtle toxicity to aquatic biota and humans. Liquid–liquid extraction, Clean-up experiment and High Performance Liquid Chromatography (HPLC) were the methods employed for the quantitative determination of the Phthalates. A study of uncontaminated water was done to establish blank levels. The sewage lagoon and the receiving stream were grossly polluted as several phthalate ester plasticizers: DMP, DEP, DPhP, DBP, DEHP, DOP and DINP were found present at monthly mean levels of between 24.02 mg/L and 139.25 mg/L in the sewage treatment lagoon and 10.41 mg/L and 80.53 mg/L in the receiving stream. The results showed higher levels of phthalate esters in the sewage lagoon compared to the receiving stream. The sewage lagoon was identified as a pollution point source into the receiving stream. Levels of phthalates obtained from the receiving stream are much higher than the water criteria of 3 μg/L phthalates recommended by the United States Environmental Protection Agency (USEPA) for the protection of fish and other aquatic life in water and the Suggested No-Adverse Effect Levels (SNAEL) of 7.5–38.5 μg/L for drinking water. This should give cause for great environmental concern. Peoples’ health downstream is at stake and so is the ‘health’ of the ecosystem.     

Application of a Larval Medaka Assay to Evaluate the Fish Safety Level in Sagami River, Japan

Physico-chemical characteristics of some river and hand-dug well waters used for drinking and domestic purposes in the oil rich Niger Delta area of Nigeria were assessed using standard methods. The concentrations of the parameters in the river water samples ranged in the following order: pH (5.6–6.9), temperature (26.90–28.60°C), turbidity (23–63 NTU), electrical conductivity (52–184 μs/cm), DO (5.4–7.2 mg/l), BOD (21–57 mg/l), TDS (6.0–217 mg/l), PO₄ ³⁻ (0.19–1.72 mg/l), SO₄ ²⁻ (25–36.8 mg/l), NO₃ ⁻ (20.3–28 mg/l), Fe (6.07–15.71 mg/l), Zn (0.04–0.24 mg/l), Pb (0.01–0.17 mg/l), Ni (0.01–0.13 mg/l), Vn (0.01–0.20 mg/l) and Hg (0.001–0.002 mg/l). The concentrations of these parameters in the hand-dug well water ranged in the following order: pH (5.7–6.8) temperature (26–30°C), turbidity (134–171 NTU), electrical conductivity (160–340 μs/cm), DO (5.4–6.4 mg/l), BOD (13–34 mg/l), TDS (110–190 mg/l), PO₄ ³⁻ (0.84–1.84 mg/l), SO₄ ²⁻ (10.6–28.1 mg/l), NO₃ ⁻ (11.3–23 mg/l), Fe (13.17–16.31 mg/l), Ni (0.01–0.02 mg/l), Vn (0.01–0.04 mg/l) and Hg (0.001–0.004 mg/l). The concentrations of BOD, turbidity, NO₃ ⁻ and Fe in the water samples were above WHO and FMENV permissible limits for safe drinking water. The results suggest that the use of such waters for drinking and domestic purposes pose a serious threat to the health of the users and calls for the intervention of government agencies.     

Distribution of heavy metals in surface water of Ranipet industrial area in Tamil Nadu, India

Ranipet industrial area is about 120 km from Chennai on Chennai-Bangalore highway and is a chronic polluted area identified by Central Pollution Control Board of India. It is one of the biggest exporting centers of tanned leather in India. The total number of industries located in and around Ranipet town are 240 tanneries along with ceramic, refractory, boiler auxiliaries plant, and chromium chemicals. Studies were carried out to find out the contamination of surface water bodies due to industrial effluents. The results reveal that the surface water in the area is highly contaminated showing very high concentrations of some of the heavy/toxic metals like Cadmium ranging from 0.2 to 401.4 μg/l (average of 51.1 μg/l), Chromium 2.4–1,308.6 (average of 247.2 μg/l), Copper 2.1–535.5 μg/l (average of 95.5 μg/l), Nickel 1.6–147.0 μg/l (average of 36.7 μg/l), Lead 6.4–2,034.4 μg/l (average of 467.8 μg/l) and Zinc 20.8–12,718.0 μg/l (average of 3,760.4 μg/l). The concentration levels of these metals are much above the permissible limits in surface water and are health hazards especially for the people working in the tannery industries. It was observed that the people in the area are seriously affected and suffering from occupational diseases such as asthma, chromium ulcers and skin diseases. Distribution of metals, their contents at different locations, and their effects on human health are discussed in this paper.     

Speciative determination of Cr (III) and Cr (VI) in dyeing waste water of Dil Creek discharge to Izmit Gulf (Izmit-Kocaeli, Turkey) by ICP-AES

Wastewater pollution in industrial areas is one of the most important environmental problems. Heavy metal pollution, especially chromium pollution in wastewater sources from dyeing and tannery has affected the life on earth. This pollution can affect all ecosystems and human health directly or by food chain. Therefore, the determination of chromium in this study is of great importance. Dil Creek is located in the eastern Marmara region and discharges into the Izmit Gulf. This water source is used for irrigation in agriculture and as drinking water for animals. In this study, a rapid, sensitive and selective method for the speciative direct determination of Cr (III) and Cr (VI) in dyeing waste water samples collected from the nearest station to Izmit Gulf of Dil Creek in May 2006 by inductively coupled plasma-atomic emission spectrometry (ICP-AES) has been developed. An analysis of a given sample is completed in about 15 min for ICP-AES the method. As the result of the chromium analysis, the limit of quantification (LOQ) for the Cr (III), Cr (VI) and total Cr were founded as 0.0111 ± 0.0002 mg/l (RSD, 1.80%), 0.0592 ± 0.0010 mg/l (RSD, 1.70%) and 0.0703 ± 0.0020 mg/l (RSD, 2.84%) respectively. In addition, the general mathematical formula has been developed to calculate the concentration of Cr(III), which can be applied to any other metal species. The result of Cr (VI) analysis indicated that water quality of Creek was IV. class quality according to the inland water classification. In order to validate the applied method, recovery studies were performed.     

Multi-level modelling of chlorination by-product presence in drinking water distribution systems for human exposure assessment purposes

During drinking water treatment and distribution, chlorine reacts with organic matter occurring in water to form various chlorination by-products (CBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). This paper presents the occurrence of THMs and HAAs in different water distribution systems (DS) of the same region and their modelling for exposure assessment purposes. This study was conducted in eight DS supplying chlorinated water to the population of Québec City, Canada. These systems differ in type of water source (i.e. surface, ground or mixed water), in treatment applied at the plant, and in size and structure of the DS. Two spatio-temporal databases for THMs and HAAs were implemented, one for model development and the other for model validation. The analysis of the data demonstrates significant seasonal and spatial variations of these compounds. A multi-level statistical modelling approach was applied to estimate the ranges for occurrence of THMs and HAAs in the eight DS (i.e. a single model for the study region for each CBP species). The modelling approach integrates available or easily measurable parameters. For both THMs and HAAs, a two-level model considering a sampling-site random effect was selected among various models initially developed. The model capacity for estimating the presence of THMs and HAAs in drinking water and its usefulness for exposure assessment purposes in the studied region was demonstrated.     

Cyanobacterial Flora from Polluted Marine Shores

Citation of cyanobacterial cultures from the shores of south west coast of Gujarat, India and their relationship with sea water quality, influenced by extensive pollutant runoff is reported in this study. Intensity of pollution was evaluated by physico-chemical analysis of water. Higher load of suspended solids (60–1000 mg l⁻¹) and nutrients (PO₄ ⁻P: 1.3–4 μmole l⁻¹ and NO₃ ⁻N: 12.5–17.8 μmole l⁻¹) were persistent throughout the analysis. Community structure is seen to be influenced by such persistent pollution. Twenty nine cyanobacterial species were isolated belonging to 9 genera of 4 families, with an elevated occurrence of Oscillatoria and Lyngbya species. No heterocystous cyanobacteria were isolated throughout the study.