Wastewater-irrigated Sites Research Articles

Heavy metal contamination through wastewater irrigation on the soil and vegetables: Impact on the nutrient content and health risks ​

The use of wastewater irrigation may contribute to the metal accumulation, and reduction of nutrient level of vegetables, which would then have an adverse effect on human health. Therefore, in the present study we investigated heavy metals contamination and its impact on nutrient quality of vegetables and health risk. The study was conducted from the agricultural fields of Varanasi distinct during the period from March 2022 to June 2023 and all the laboratory work was carried in the department of Botany, Banaras Hindu University. Heavy metal concentrations in water, soil, and vegetable samples were measured using an atomic absorption spectrophotometer. The physiochemical property (pH), daily intake of metal, metal pollution index and health quotient were also calculated according to the published protocols. All heavy metal were found in higher concentrations in the wastewater irrigated soil that control site. The Lohta site had the highest concentration of heavy metals in the vegetables, followed by Dinapur, and least at control site (BHU). The highest concentration of metals (Cu, Zn, and Pb) were found in the leafy vegetables (S. oleracea and A. esculentus) whereas lowest in fruity vegetables (P. vulgaris). The rise in the Metal Pollution Index (MPI) also provided evidence for the greater metal content of these vegetables. The S. oleracea was found to have the highest DIM (0.061 g/g) while P. vulgaris had the lowest (0.007 g/g). HQ values of these metals were found greater than one ( greater than 1) for both children and adults on the ingestion of the vegetables of wastewater irrigated sites. Further, nutrient contents (Na, Mg, Ca) were also declined in the vegetables of wastewater irrigated site when compared to control site. These findings suggest that the consumption of such vegetables leads to compromised health and might be associated with severe health risk in the human.

Heavy Metal Contamination Status of Water, Agricultural Soil, and Plant in the Semiarid Region of Kandahar, Afghanistan

Agricultural irrigation using wastewater containing heavy metals (HM) might impose risks in bioaccumulation in foods. The current study was performed to assess the status of HM in terms of water-soil–plant systems in Kandahar, Afghanistan, where industrial and domestic wastewater was partially reused for irrigation. Water, soil, and plant samples were collected from wastewater sites in Haji-Arab (HA), Bala-Karz (BKZ), and Mahal-e-Nejat (MN) in comparison with those from a freshwater-irrigated site in Char-Bagh (CB). The HM levels in unfiltered water samples remained lower than the World Health Organization (WHO) and Food and Agriculture Organization (FAO) permissible values, but the HM concentrations in soil and crops were higher at the HA, BKZ, and MN (wastewater-irrigated sites) than those at the CB site (freshwater-irrigated site). Lead (Pb) levels were high in soils (43–83 mg/kg) and crops (18–36 mg/kg) and extremely exceeded the safe limits even for those crop samples cultivated in the freshwater-irrigated site. Continuous wastewater irrigation increased the HM concentration in water, soil, and plants, but the Pb pollution was found to be ascribed to the minerals in that area since the underground water was showing high Pb levels. The bioaccumulation of HM in the studied sites was related to the cultivated crops and correlated with the land use in the watershed area. This study is important in understanding the risks associated with HM and exercising prudence when applying various irrigation resources in Afghanistan.

Effects of diverse irrigation with wastewater in soil and plants: assessing the risk of metal to the animal food chain

In District Jhang, farmers use municipal wastewater to irrigate fodder crops as an alternative source to the deficient availability of fresh water. Therefore, the present study selected the three irrigation sources in District Jhang (canal water, ground water and municipal wastewater) to study the iron (Fe) concentration in the soil, fodder crops and ultimately their transfer into the animal body. Analysed Fe concentration varied as 16.40-27.53mg/kg in soil samples, 19.72-30.34mg/kg in fodder crops and 2.49-5.11mg/kg in animals. Analysed Fe concentration in soil was higher on the wastewater irrigation site while canal water-irrigated fodder crop Zea mays exhibit the higher Fe concentration. In animal samples, higher Fe concentration was observed in the cow blood (4.09mg/l), cow hairs (3.39mg/kg) and cow faeces (5.11mg/kg). Results of pollution load index (0.288-0.484mg/kg) and enrichment factor (0.112-0.197mg/kg) indicated that Fe concentration was minimally dispersed and enriched in these sites. Health risk and daily intake values were observed between the 0.029-0.059 and 0.042-0.084mg/kg/day. Bio-concentration factor (0.834-1.47mg/kg) for Fe which was greater than 1 explains that Fe contamination was transferred from the soil to fodder tissues and may raise health issues in the grazing animals if they are continuously exposed to these contaminated forages. Wastewater irrigation in study area has increased the Fe content in soil-plant environment that is a risking factor for animal and human health. Hence, this study recommended that wastewater should be treated prior to their irrigation on agricultural lands.

Determination of contaminants of emerging concern and their transformation products in treated-wastewater irrigated soil and corn

In many parts of the world, clean water has become increasingly scarce. Irrigation of agricultural land with treated wastewater is commonly used in response to water shortages but there is concern about the environmental fate and transport of contaminants present in the irrigation wastewater. This study aimed to examine the presence of wastewater sourced contaminants in soil and field grown corn (Zea mays) crops spray irrigated with treated wastewater. Soil, corn grain, leaves, and roots were sampled and tested from a long-term wastewater irrigation site as well as a non-irrigated control site in close geographic proximity. Samples were analyzed using comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry (GC × GC-TOFMS) and both targeted and non-targeted analyses were conducted to determine chemical differences between the wastewater irrigated and control samples. Target compounds detected and quantified in the samples include herbicides, phthalates, and polycyclic aromatic hydrocarbons. Non-targeted analysis showed chemical differences between each the wastewater irrigated and control samples. Furthermore, new chloro-dimethyl-benzotriazole compounds, which are suspected to be transformation products created by the chlorine disinfection process of the wastewater treatment plant, were tentatively identified in the wastewater effluent. Twenty of these new benzotriazoles were detected and semi-quantified in the wastewater irrigated soil samples at a maximum concentration of 472 ng/g. Eight of the most abundant benzotriazoles were also detected in the corn roots at concentrations up to 56 ng/g.

Effects of Fire Phoenix (a genotype mixture of Fesctuca arundinecea L.) and Mycobacterium sp. on the degradation of PAHs and bacterial community in soil.

Phytomicrobial remediation technology of PAH-contaminated soils has drawn great attention due to its low-cost, eco-friendly, and effective characteristics, but the mechanism underlying the removal of PAHs by rhizosphere in wastewater-irrigated soil is so far not clear. To evaluate the dissipation of PAHs and the shifts of bacterial community structure under plant-microorganism symbiotic system in an agricultural soil, a rhizo-box experiment with Fire Phoenix (a genotype mixture of Fesctuca arundinecea L.) or/and inoculated Mycobacterium sp. was conducted for 60 days. The changes of bacterial community structure and the contents of PAHs were analyzed by denaturing gradient gel electrophoresis (DGGE) and high-performance liquid chromatography (HPLC), respectively. The results showed that the removal rate of PAHs in phytomicrobial combined treatment was 53.7% after 60 days. The PAH-degraders were dominated by Microbacterium sp., Sphingomonas sp., Mycobacterium sp., and Flavobacterium sp. The plant of Fire Phoenix induced the appearance of Pseudomonas sp. and TM7 phylum sp. oral clone. The highest of bacterial diversity index was observed in unrhizosphere soils (MR-), rather than that in rhizosphere soils (MR+). In combination, phytomicrobial combined treatment of Fire Phoenix and Mycobacterium strain enhanced the removal rate of PAHs and changed the structure of bacterial community and bacterial diversity. Bacterial community has great effect on PAH degradation in PAH-contaminated soil from the wastewater-irrigated site. Our study can provide support information for PAH degradation enhancement by the synergetic effect of Fire Phoenix and Mycobacterium sp.

Proximate Compositions and Health Risk Evaluation of Heavy Metal Uptake by Vegetables Grown at a Waste –Water Irrigated Site in Fct, Abuja, Nigeria

The purpose of the study was to evaluate some proximate compositions and health risk of heavy metal uptake by vegetables grown at a waste-water irrigated sites in FCT, Abuja. The study was carried in dry seasons between 2015 and 2017. Two different types of vegetable samples (Lagos Spinach- Celosia argentea and African Egg-plant- Solanum macrocarpon) were collected simultaneously from three irrigated farm sites. Heavy metal levels were quantified using Atomic Absorption Spectrophotometer (AAS). Other parameters were determined using standard methods. The levels of heavy metals in vegetables varied according to sites. Proximate composition in both vegetable leaves recorded higher mean values for total ash (8.65-8.97), crude fibre (10.83-11.25), protein (4.96-5.08), Fat (3.05-3.29) and dry matter (65.58-68.85) indicating that they were rich in nutrients that promote healthy living. The mean levels of Zn (3.36±0.50) and Ni (0.03±0.01) in Lagos Spinach ; and Zn (2.80±0.36) and Ni (0.04±0.02) in African Egg-plant were generally lower than the FAO/WHO permissible limits except for Fe (14.96±0.86),(15.81±0.89) and Pb (1.12±0.11), (1.31±0.11) in both vegetables that were significantly higher (P<0.05) . Lagos Spinach recorded lower Metal Pollution Index (10.35) while African Egg-plant had the highest value (12.18) suggesting that these vegetables may present more health risk to the consumers of these vegetable. Daily Intake values of Fe (0.089), Zn (0.020), Ni (0.001) and Pb (0.006) in Lagos Spinach and Fe (0.094), Zn (0.017), Ni (0.001) and Pb (0.008) in African Egg-plant were below the WHO/FAO and USEPA permissible limits. However, Health risk index of heavy metals in vegetable samples were less than 1 indicating no significant health risk associated with the consumption of vegetables by the consumers.

Non-enzymatic Antioxidants and Transaminases Constitute Homeostatic Mechanisms for Some Egyptian Vegetables Irrigated with Treated Wastewater

To evaluate the effect of irrigation with treated wastewater on some Egyptian leafy vegetables, some non-enzymatic antioxidants and transaminases were determined. This study was conducted at wastewater irrigated site (Arab Al-Olyqat), 30 kilometers from Cairo, while 3 kilometers was the distance between control (Nile River canal, fresh water, irrigated site; Shibeen Al-Kanater) and treated wastewater irrigated site. Concentrations of total phenols and L-ascorbic acid were significantly decreased in parsley and spinach. Total phenols of cabbage and L-ascorbic acid of garden rocket were significantly decreased, while those of lettuce were significantly increased compared to their controls due to irrigation with treated wastewater. Irrigation with treated wastewater resulted in significant increases of proline in cabbage and parsley and significant decreases in garden rocket and spinach. Free thiol compounds showed significant decreases in spinach, parsley and cabbage, while significant increases in garden rocket and lettuce were recorded. Vegetables irrigated with treated wastewater showed significant increases in the activity of GOT or (AST) compared to their controls. Activity of GPT increased significantly in lettuce by 111.6 % and decreased in parsley by 40.0% due to irrigation with treated wastewater.

Vadose Zone Transport of Natural and Synthetic Estrogen Hormones at Penn State's “Living Filter” Wastewater Irrigation Site

The concentrations listed in the “Effluent Analysis” section were incorrectly given with incorrect units, μg L−1. The correct units are ng L−1. The revised paragraph with the corrected units is given here. Measured concentrations in the effluent varied for each estrogen. For 17β-estradiol, the average concentration in the effluent was 8.43 ± 3.55 ng L−1. The average estrone concentration was 17.0 ± 8.37 ng L−1, and the average 17α-ethynylestradiol concentration was 6.76 ± 4.49 ng L−1. For all three estrogens, measured concentrations varied between sprinkler heads. The estrogen concentrations measured in the cropped sprinkler heads ranged from 7.78 to 28.71 ng L−1, and the concentrations measured in the forested sprinkler heads ranged from below detection limit to 11.01 ng L−1. These data confirm that even after primary and secondary treatment, estrogens are present in the effluent at concentrations that can affect organisms. Without land application, effluent would be directly discharged into streams. These data highlight one possible benefit of land-based wastewater application: it can be used as a form of hormone removal.

Public health risk assessment of chromium intake from vegetable grown in the wastewater irrigated site in Bangladesh

There are many potential risks to human health from heavy metal contamination of vegetables resulting from wastewater irrigated sites. This study was carried out to assess the concentration of chromium (Cr) and the risk to human health by chromium through the intake of locally grown vegetables collected from wastewater irrigated agricultural fields. Twenty-seven samples of 9 (nine) different types of vegetables were analyzed by an Atomic Absorption Spectrometer (AAS) (Varian AAS 240 F S). The range of chromium concentration in wastewater irrigated vegetables was ND (Not detected) -4.14mg/kg. The highest mean concentration of chromium (4.14 mg/kg) was detected in radish. The mean concentration of chromium in all the vegetables was within the safe limits of WHO/FAO except radish which was much higher than the standard. Health risk index for chromium contamination in all vegetables was less than 1 for both adults and children which cause no risk to the local population. Among all vegetables tested, the highest intake value of chromium was from consumption of radish for both adults and children. The lower values of health risk index indicated chromium contamination in the wastewater irrigated vegetables that cause less negative impact on human health.

Vadose Zone Transport of Natural and Synthetic Estrogen Hormones at Penn State's "Living Filter" Wastewater Irrigation Site.

The increase in endocrine-disrupting compounds in the environment has generated research focused on the behavior of these compounds in natural soil and water ecosystems. To understand how estrogens behave in the soil environment as a result of 25+ yr of wastewater irrigation, soils from Penn State's "Living Filter" wastewater irrigation site were extracted and analyzed for two natural estrogens (17β-estradiol and estrone) and one synthetic estrogen (17α-ethynylestradiol). Soil estrogen concentrations were compared for two independent variables: type of land cover and sampling time. Soils were sampled from cropped and forested land areas, and soils were sampled 2 d and 3 wk after a single 12-h effluent irrigation event. A nonirrigated control site was sampled to provide natural background data. For 17β-estradiol, the nonirrigated mean concentration was 0.68 ± 0.11 ng cm, and the irrigated values, including samples from both land areas and time frames, ranged from 0.99 ± 0.11 to 1.82 ± 0.69 ng cm. For estrone, the nonirrigated mean concentration was 2.36 ± 0.22 ng cm, and the irrigated values, including samples from both land areas collected and time frames, ranged from 2.18 ± 0.20 to 6.24 ± 3.14 ng cm. The 17α-ethynylestradiol nonirrigated mean concentration was 0.47 ± 0.40 ng cm. The irrigated values, including samples from both land areas and time frames, ranged from 0.25 ± 0.06 to 1.37 ± 0.39 ng cm. This study found that time of sampling, land cover, and irrigation can affect estrogen concentrations in soils, resulting in levels that exceed natural background and require improvements in management practices.

Hazardous of Waste Water Irrigation on Quality Attributes and Contamination of Citrus Fruits

There is an increasing concern regarding the potential health risks associated with consuming crops grown on sewage irrigated soils. The present study was carried out to assess levels of different heavy metals like iron, manganese, copper and zinc, in citrus fruits irrigated with water from two places in Jeddah; namely Al Hada site (as a control) and Al Musk Lake (as a contaminated site). Heavy metal concentrations were several fold higher in all the collected samples (water, soils and fruits) from wastewater irrigated site compared to potable water irrigated ones. Fruits collected from contaminated soils had lower firmness (30% less that that collected from the reference site), while their size, weight and their soluble solids content (SSC) increased up to 3.5 cm in diameter, 22% and 14%, respectively. We found central axis of the orange fruits irrigated with wastewater was infected by the fungus Alternaria citri in the form of a rot, with hardly any external symptoms. Assessment of water and soils collected from Al Musk Lake indicated that they are not suitable for any uses. Moreover, these higher levels of metal pollution in the wastewater irrigated site presented a significant threat of negative impact on human health. The results presented demonstrate that there is a risk associated with consumption of fruits and vegetables irrigated with wastewater, with the fruits still looking apparently healthy and growing well despite accumulating heavy metals to concentrations which substantially exceed maximum values considered safe for human consumption

Influence of the sewage irrigation on the agricultural soil properties in Tongliao City, China

Increasing shortages of fresh water has led to greater use of treated wastewater for irrigation of crops. This study evaluates the spatial variability of soil properties after irrigation with wastewater and freshwater. Geostatistical techniques were used to identify the variability of soil properties at the different sites. A set of physical and chemical soil properties were measured including total nitrogen (TN), total phosphorus (TP), organic matter (OM) and soil moisture. The TN concentration levels varied from 567 to 700 mg·kg−1, while OC levels ranged from 7.3 to 16.3 mg·kg−1 in wastewater-irrigated zones. The concentration levels of TP were between 371.53 and 402.88 mg·kg−1 for the wastewater-irrigated sites. Wastewater irrigation resulted in higher TN, TP and OM concentrations by 18.4%, 8% and 25%, respectively. The highest TN and OM occurred along the wastewater trunk. It was also observed that nitrogen concentrations correlate with the soil’s organic matter. The increase of salinity may be associated with the increase of pH, which might suggest that a reduction of pH will be beneficial for plant growth due to the decrease of salinity. The average concentrations of nitrogen in topsoil were higher than those in subsurface soils in irrigated areas. Such differences of the N profile might be due to variations in organic matter content and microbial populations. Consistent with TN and OM, soil C:N decreased significantly with an increase of depth. This phenomenon possibly reflects a greater degree of breakdown and the older age of humus stored in the deeper soil layers. The analysis of pH levels at different depths for the three sites showed that pH values for wastewater irrigation were slightly lower than the controlled sites at the same depths.

Assessing environmental impacts of reclaimed wastewater irrigation in paddy fields using bioindicator

Irrigation water quality influences many aspects of agroecosystems, but less is known about how complex microbial and biological communities respond to changing water quality due to causes such as reuse irrigation. The objectives of this study are to monitor and assess the environmental impacts of reclaimed wastewater irrigation on water quality and soil that might cause potential health hazards and to assess its agro-environmental effects. Two sites, which are irrigated by filtered wastewater after UV (Ultraviolet) treatment and from an agricultural reservoir that satisfied the agricultural water quality standards of Korea, were selected as treatment and control, respectively. The environmental impacts of irrigation water quality on paddy soil, microorganisms, and arthropods were investigated. Monitoring results for water, soil, health risks, and eco-environments of the reclaimed wastewater irrigation site demonstrated no adverse effects in the paddy field. This research showed that reclaimed wastewater irrigation did not present significant environmental risks for the rice paddy agroecosystem, although long-term monitoring is needed to fully characterize its effects.

Effects of Waste Water Irrigation on Physical and Biochemical Characteristics of Soil and Metal Partitioning in Beta vulgaris L.

The present study deals with the assessment of changes in physical and biochemical characteristics of soil and metal partitioning in Beta vulgaris L. grown in farmer’s fields irrigated with waste water in Dinapur and Lohta areas of Varanasi, India, during December to February, 2007–2008 and 2008–2009. Nutrient concentrations, organic carbon, microbial biomass, C, N, and P, enzymatic activities and heavy metal concentrations in soil and plant parts were estimated at waste water (DW1, DW2 and LW) and clean water-irrigated sites (DC and LC). Sites receiving waste water irrigation showed an increase in organic C by 36 and 64 % and in available phosphorus by 15 and, 21 % at DW1 and DW2 sites compared to DC and 88 and 29 % at LW compared to LC during the first year. Dehydrogenase and urease activities increased two to threefold at waste water-irrigated sites compared to the respective clean water-irrigated ones during both the years of study. Microbial biomass (C, N, and P) and concentrations of exchangeable cations (Na+, K+, and Ca+2) also showed increments varying from two to threefold at waste water-irrigated sites. During both the years, total heavy metal concentration in soil was the highest for Mn followed by Zn, Pb, Ni, Cu, Cr, and Cd at Dinapur, whereas at Lohta the trend was Mn, Zn, Cr, Pb, Cu, and Cd. The accumulation of heavy metals in the plants was several-fold higher in roots and shoots at waste water-irrigated sites, and Cd, Pb, and Ni were above the safe limits in edible tissues. Lower metal concentrations were recorded at DW1 site compared to DW2 and LW sites. The study suggests that waste water irrigation led to beneficial changes in physico-chemical and biological properties of the soil, but increased the soil contamination of heavy metals. However, the intermittent use of clean water in such areas may not only reduce the metal contamination in the plants but will also maintain soil fertility.

Heavy metal accumulation in vegetables grown in a long-term wastewater-irrigated agricultural land of tropical India

In the present study, the magnitude of contamination of vegetables with heavy metals (Pb, Zn, Cd, Cr, Cu and Zn) was determined in a long-term wastewater-irrigated agricultural land. Heavy metal concentrations in vegetables were several folds higher in wastewater-irrigated site compared to clean water-irrigated area. The wastewater-irrigated crops analysed in this study are heavily contaminated with heavy metals. Concentrations of Pb, Zn, Cd and Cr in all the sewage-fed vegetables were beyond the safe limit of FAO/WHO and Indian standard. Contamination is at its highest level in radish and spinach. Daily intake values of Pb, Cd and Ni through consumption of sewage-fed vegetables exceeded the recommended oral dose of metal for both adult and children. The study concludes that wastewater irrigation led to accumulation of heavy metals in vegetables causing potential health risk to consumers.

Health risk assessment of heavy metals via dietary intake of foodstuffs from the wastewater irrigated site of a dry tropical area of India

The present study was conducted to assess the risk to human health by heavy metals (Cd, Cu, Pb, Zn, Ni and Cr) through the intake of locally grown vegetables, cereal crops and milk from wastewater irrigated site. Milk is not directly contaminated due to wastewater irrigation, but is an important route of food chain transfer of heavy metals from grass to animals. Heavy metal concentrations were several fold higher in all the collected samples from wastewater irrigated site compared to clean water irrigated ones. Cd, Pb and Ni concentrations were above the ‘safe’ limits of Indian and WHO/FAO standards in all the vegetables and cereals, but within the permissible limits in milk samples. The higher values of metal pollution index and health risk index indicated heavy metal contamination in the wastewater irrigated site that presented a significant threat of negative impact on human health. Rice and wheat grains contained less heavy metals as compared to the vegetables, but health risk was greater due to higher contribution of cereals in the diet. The study suggests that wastewater irrigation led to accumulation of heavy metals in food stuff causing potential health risks to consumers.

Concentrations and bioaccessibility of polycyclic aromatic hydrocarbons in wastewater-irrigated soil using in vitro gastrointestinal test

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants and contribute to the pollution of soil environment. Soil ingestion is of increasing concern for assessing health risk from PAH-contaminated soils because soil ingestion is one of the potentially important pathways of exposure to environmental pollutants, particularly relevant for children playing at contaminated sites due to their hand-to-mouth activities. In vitro gastro-intestinal tests imitate the human digestive tract, based on the physiology of humans, generally more simple, less time-consuming, and especially more reproducible than animal tests. This study was conducted to investigate the level of PAH contamination and oral bioaccessibility in surface soils, using physiologically based in vitro gastro-intestinal tests regarding both gastric and small intestinal conditions. Wastewater-irrigated soils were sampled from the metropolitan areas of Beijing and Tianjin, China, which were highly contaminated with PAHs. Reference soil samples were also collected for comparisons. At each site, four soils were sampled in the upper horizon at the depth of 0-20 cm randomly and were bulked together to form one composite sample. PAH concentrations and origin were investigated and a physiologically based in vitro test was conducted using all analytical grade reagents. Linear regression model was used to assess the relationship between total PAH concentrations in soils and soil organic carbon (SOC). A wide range of total PAH concentrations ranging from 1,304 to 3,369 mug kg(-1) in soils collected from different wastewater-irrigated sites in Tianjin, while ranging from 2,687 to 4,916 mug kg(-1) in soils collected from different wastewater-irrigated sites in Beijing, was detected. In general, total PAH concentrations in soils from Beijing sites were significantly higher than those from Tianjin sites, indicating a dominant contribution from both pyrogenic and petrogenic sources. Results indicated that the oral bioaccessibility of PAHs in small intestinal was significantly higher (from P < 0.05 to P < 0.001) than gastric condition. Similarly, the oral bioaccessibility of PAHs in contaminated sites was significantly higher (from P < or = 0.05 to P < 0.001) than in reference sites. Individual PAH ratios (three to six rings), a more accurate and reliable estimation about the emission sources, were used to distinguish the natural and anthropogenic PAH inputs in the soils. Results indicated that PAHs were both pyrogenic and petrogenic in nature. The identification of PAH sources and importance of in vitro test for PAH bioaccessibility were emphasized in this study. The oral bioaccessibility of individual PAHs in soils generally decreased with increasing ring numbers of PAHs in both the gastric and small intestinal conditions. However, the ratio of bioaccessibility of individual PAHs in gastric conditions to that in the small intestinal condition generally increased with increasing ring numbers, indicating the relatively pronounced effect of bile extract on improving the bioaccessibility of PAHs with relatively high ring numbers characterized by their high K ( ow ) values. Similarly, total PAH concentrations in soils were strongly correlated with SOC, indicating that SOC was the key factor determining the retention of PAHs in soils. Soils were contaminated with PAHs due to long-term wastewater irrigation. PAHs with two to six rings showed high concentrations with a significant increase over reference soils. Based on the molecular indices, it was suggested that PAHs in soils had both pyrogenic and petrogenic sources. It was also concluded that the oral bioaccessibility of total PAHs in the small intestinal condition was significantly higher than that in the gastric condition. Furthermore, the bioaccessibility of individual PAHs in soils generally decreased with the increasing ring numbers in both the gastric and small intestinal conditions. It is suggested that more care should be given while establishing reliable soil criteria for PAHs, especially concerning the health of children who may ingest a considerable amount of PAH-contaminated soil via outdoor hand-to-mouth activities.

Importance of Waste Stabilization Ponds and Wastewater Irrigation in the Generation of Vector Mosquitoes in Pakistan

The objective of the current study was to investigate the role of waste stabilization ponds (WSP) and wastewater-irrigated sites for the production of mosquitoes of medical importance. Mosquito larvae were collected fortnightly from July 2001 to June 2002 in Faisalabad, Pakistan. In total, 3,132 water samples from WSP and irrigated areas yielded 606,053 Culex larvae of five species. In addition, 107,113 anophelines, representing eight species were collected. Anopheles subpictus (Grassi) and Culex mosquitoes, especially Culex quinquefasciatus (Say) and Culex tritaeniorhynchus (Giles), showed an overwhelming preference for anaerobic ponds, which receive untreated wastewater. Facultative ponds generated lower numbers of both Anopheles and Culex mosquitoes, whereas the last ponds in the series, the maturation ponds, were the least productive for both mosquito genera. An. subpictus and Anopheles stephensi (Liston) were the dominant Anopheles species in wastewater-irrigated sites, with Anopheles culicifacies (Giles) recorded in low numbers. This was also the pattern in nearby sites, irrigated with river water. Among the Culex species, Cx. tritaeniorhynchus was by far the most frequently recorded in both wastewater- and river water-irrigated sites with Cx. quinquefasciatus as the second most abundant species but restricted to wastewater-irrigated areas. Univariate logistic regression analysis showed that presence of An. subpictus and Culex mosquitoes was significantly associated with emergent grass vegetation and low salinity. Regular removal of emergent grass along the margins of the anaerobic ponds and changes in the concrete design of the ponds are likely to reduce the mosquito production, especially of Culex species.

Phosphorus Leaching at Cold Temperatures as Affected by Wastewater Application and Soil Phosphorus Levels

Land application of wastewater in the northern-tier United States during winter months has been suggested as a means to reduce cost of building storage lagoons. A study was initiated in 1996 to assess land application of potato-processing wastewater on a 120-ha field at Park Rapids, MN. One objective of this study was to evaluate the effects of soil P levels and temperature on P leaching in soil columns. In this paper, we report the P sorption, desorption, and leaching characteristics of a high-P (>200 mg kg(-1)) and a low-P (<25 mg kg(-1)) surface soil from the wastewater irrigation site. The leaching experiment was done with wastewater at 4 +/- 2 or 10 +/- 2 degrees C. The high-P soil resulted in an equilibrium P concentration of 8.0 mg L(-1) compared with 0.14 mg L(-1) for the low-P soil. When low-P wastewater was applied to the high-P soil, the soil acted as a P source, and the total phosphorus (TP) concentration in the leachate was 3.5 times higher than the input TP concentration (C0). When high-P wastewater was applied to the high-P soil, the soil acted as a P sink retarding the TP concentration in the leachate by 80%. Phosphorus desorption was higher at 10 degrees C compared with 4 degrees C. The results showed that depending on P levels of the soil and the wastewater, reduction or increase in leachate P will occur below the surface soil. However, further mobility of this P under field conditions will depend on the volume and rate of percolating water as well as the sorption-desorption characteristics of the subsoil.

Source Bioaerosol Concentration and rRNA Gene-Based Identification of Microorganisms Aerosolized at a Flood Irrigation Wastewater Reuse Site

Reuse of partially treated domestic wastewater for agricultural irrigation is a growing practice in arid regions throughout the world. A field sampling campaign to determine bioaerosol concentration, culturability, and identity at various wind speeds was conducted at a flooded wastewater irrigation site in Mexicali, Baja California, Mexico. Direct fluorescent microscopy measurements for total microorganisms, culture-based assays for heterotrophs and gram-negative enteric bacteria, and small-subunit rRNA gene-based cloning were used for microbial characterizations of aerosols and effluent wastewater samples. Bioaerosol results were divided into two wind speed regimens: (i) below 1.9 m/s, average speed 0.5 m/s, and (ii) above 1.9 m/s, average speed 4.5 m/s. Average air-borne concentration of total microorganisms, culturable heterotrophs, and gram-negative enteric bacteria were, respectively, 1.1, 4.2, and 6.2 orders of magnitude greater during the high-wind-speed regimen. Small-subunit rRNA gene clone libraries processed from samples from air and the irrigation effluent wastewater during a high-wind sampling event indicate that the majority of air clone sequences were more than 98% similar to clone sequences retrieved from the effluent wastewater sample. Overall results indicate that wind is a potential aerosolization mechanism of viable wastewater microorganisms at flood irrigation sites.