Farm Exposures and Allergic Disease Among Children Living in a Rural Setting.

OBJECTIVES: The purpose of this study was to examine the association between farm exposures and asthma and allergic disease in children while also highlighting the experiences of non-farm rural children. METHODS: This was a cross-sectional analysis of data collected from across the province of Saskatchewan, Canada in 2014. Surveys were completed by parents of 2275 rural dwelling children (farm and non-farm) aged 0 to 17 years within 46 rural schools. Questionnaires were distributed through schools for parents to complete. RESULTS: Asthma prevalence was 7.6%, of which 29.5% of cases were allergic. After adjustment for potential confounders, home location (farm vs non-farm) and other farm exposures were not associated with asthma and asthma phenotypes. Those who completed farm safety education were more likely to have asthma (11.7% vs. 6.7%; p = .001) compared to children without asthma. In sub-analyses among 6-12-year-old children, boys were more likely to have asthma (non-allergic) and use short-acting beta-agonists compared to girls. Doing farm work in the summer was associated with an increased risk of asthma [adjusted OR (aOR) = 1.71 (1.02-2.88); p = .041]. Doing routine chores with large animals was associated with an increased risk of asthma [aOR = 1.83 (1.07-3.15); p = .027] and allergic asthma [aOR = 2.37 (95%CI = 1.04-5.40); p = .04]. CONCLUSION: The present study showed that the prevalence of asthma and asthma phenotypes were similar between farm and non-farm rural children. There did not appear to be differential involvement in farming activities between those with and without asthma although those with asthma had more training suggesting possible attempts to mitigate harm from farm exposures.

The interplay of larval age and particle size regulates micro-polystyrene biodegradation and development of Tenebrio molitor L.

Microplastics, tiny plastic fragments from 1 µm to 5 mm, are widespread globally, even in remote environments. Due to their small sizes, they are easily ingested by organisms and contaminate the food chain. Recently, the biodegradation of some recalcitrant plastics by larva of Tenebrio molitor L. (mealworm) has been reported. However, the effects of microplastic feeding on them are limited. In our study, we selected rigid micro-polystyrene (MPS) as the model plastic to investigate the influences of particle size and larval age on plastic consumption and degradation, and the effects of microplastic feeding on the survival and development of mealworms at different larval ages. The smaller the microplastic fragment was, the more plastics the mealworms consumed, though there was a limit on particle size. Mealworms of three-month-old had the highest consumption rate. Both depolymerization and modification on the functional groups were only observed in frass excreted by three-month old mealworms. Additionally, mealworms cofed with wheat bran and MPS of this age had comparable mortality, larval growing curve and pupation distribution as the control group with wheat bran. Our results demonstrated that mealworms in this larval stage had the greatest resistance to high doses of microplastic feeding. We suggested that microplastic waste could be provided to three-month old mealworms as half replacement of bran diet to result in the greatest plastic consumption and degradation.

[Prospective cohort study on the risks of pre-pregnancy overweight, excessive gestational weight gain on macrosomia].

Objective: To investigate the risks of pre-pregnancy overweight, excessive gestational weight gain on macrosomia. Methods: We conducted one hospital-based cohort study, focusing on pregnant women from January 2015. All pregnant women attending to this hospital for maternal check-ups, were included in our cohort and followed to the time of delivery. Data related to general demographic characteristics, pregnancy and health status of those pregnant women, was collected and maternal pre-pregnant BMI and maternal weight gain were calculated. Logistic regression was used to explore the risk difference of pre-pregnancy BMI, excessive gestational weight gain on macrosomia. Results: The overall incidence of macrosomia in our cohort appeared as 6.6% (149/2 243). After adjusting the confounding factors including age and histories on pregnancy, pre-pregnancy overweight/obesity was associated with higher risks of macrosomia (OR=3.12, 95%CI: 1.35-7.22, P=0.008; OR=2.99, 95%CI: 1.17-7.63, P=0.022) when comparing to those with normal pre-pregnancy weight. Cesarean delivery and sex of the offspring were associated with higher risk of macrosomia, while excessive gestational weight gain showed no significant difference (OR=1.41, 95%CI: 0.96-2.09, P=0.084). Our data showed that Macrosomia was statistically associated with gestational weight gain (P=0.002). After controlling parameters as age, history of pregnancy and related complications of the pregnant women, results from the logistic regression showed that women with gestational inadequate weight gain having reduced risks to deliver macrosomia, when compared to those pregnant women with adequate weight gain (OR=0.52, 95%CI: 0.30-0.90, P=0.019). Conclusion: Pre-pregnancy overweight and obesity were on higher risks to macrosomia.

Subtropical urban turfs: Carbon and nitrogen pools and the role of enzyme activity.

Urban grasslands not only provide a recreational venue for urban residents, but also sequester organic carbon in vegetation and soils through photosynthesis, and release carbon dioxide through respiration, which largely contribute to carbon storage and fluxes at regional and global scales. We investigated organic carbon and nitrogen pools in subtropical turfs and found that dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) were regulated by several factors including microbial activity which is indicated by soil enzymatic activity. We observed a vertical variation and different temporal patterns in both soil DOC, DON and enzyme activities, which decreased significantly with increasing soil depths. We further found that concentration of soil DON was linked with turf age. There were correlations between grass biomass and soil properties, and soil enzyme activities. In particular, soil bulk density was significantly correlated with soil moisture and soil organic carbon (SOC). In addition, DOC correlated significantly with DON. Significant negative correlations were also observed between soil total dissolved nitrogen (TDN) and grass biomass of Axonopus compressus and Zoysia matrella. Specifically, grass biomass was significantly correlated with the soil activity of urease and ß-glucosidase. Soil NO3-N concentration also showed negative correlations with the activity of both ß-glucosidase and protease but there were no significant correlations between cellulase and soil properties or grass biomass. Our study demonstrated a relationship between soil C and N dynamics and soil enzymes that could be modulated to enhance SOC pools through management and maintenance practices.

Occurrence of antibiotics and antibiotic resistance genes in soils from wastewater irrigation areas in the Pearl River Delta region, southern China.

The occurrence and distribution of tetracycline (TC) and sulfamethazine (SMZ), and the corresponding antibiotic resistance genes (ARGs) were investigated in six agricultural sites in the Pearl River Delta (PRD) region in southern China. Irrigation water and irrigated soils at two different depths (0-10 and 10-20cm) were analyzed. The total concentrations of TC and SMZ in irrigation water ranged from 69.3 to 234ng/L and from 4.00 to 58.2ng/L, respectively, while the total concentrations of TC and SMZ in irrigated soils ranged from 5.00 to 21.9µg/kg and from 1.30 to 4.20µg/kg, respectively. After long-term irrigation with domestic and fishpond wastewater in the field, the residual TC and SMZ and their corresponding ARGs in soils were significantly higher in fishpond-irrigated soils (Dongguan and Shenzhen) than in domestic wastewater-irrigated soils (Foshan, Guangzhou, Huizhou and Zhongshan). The concentrations of antibiotics and their ARGs were significantly higher in irrigation water than in irrigated soils, which indicated that wastewater was the primary source of antibiotics in the soil environments. The domestic and fishpond wastewater were important repositories of antibiotics and their ARGs, which require effective treatment before their discharge into the environment. Other factors such as soil physicochemical properties, manure application, irrigation water sources and cropping patterns also affect the antibiotic concentrations and ARG abundances. The residual antibiotic concentrations statistically correlated with the corresponding ARGs in irrigation water and irrigated soils, both of which decreased with increasing soil depth, indicating that the concentration of antibiotics in the environment exerted a selection pressure on the microorganisms in the environment.

Transfer of antibiotics from wastewater or animal manure to soil and edible crops.

Antibiotics are added to agricultural fields worldwide through wastewater irrigation or manure application, resulting in antibiotic contamination and elevated environmental risks to terrestrial environments and humans. Most studies focused on antibiotic detection in different matrices or were conducted in a hydroponic environment. Little is known about the transfer of antibiotics from antibiotic-contaminated irrigation wastewater and animal manure to agricultural soil and edible crops. In this study, we evaluated the transfer of five different antibiotics (tetracycline, sulfamethazine, norfloxacin, erythromycin, and chloramphenicol) to different crops under two levels of antibiotic-contaminated wastewater irrigation and animal manure fertilization. The final distribution of tetracycline (TC), norfloxacin (NOR) and chloramphenicol (CAP) in the crop tissues under these four treatments were as follows: fruit > leaf/shoot > root, while an opposite order was found for sulfamethazine (SMZ) and erythromycin (ERY): root > leaf/shoot > fruit. The growth of crops could accelerate the dissipation of antibiotics by absorption from contaminated soil. A higher accumulation of antibiotics was observed in crop tissues under the wastewater treatment than under manure treatment, which was due to the continual irrigation that increased adsorption in soil and uptake by crops. The translocation of antibiotics in crops mainly depended on their physicochemical properties (e.g. log Kow), crop species, and the concentrations of antibiotics applied to the soil. The levels of antibiotics ingested through the consumption of edible crops under the different treatments were much lower than the acceptable daily intake (ADI) levels.

Fate of antibiotics in soil and their uptake by edible crops.

Antibiotics are bioactive substances, and their use as human and animal medicines for illness prevention, disease treatment and growth promotion has increased in recent decades. They are excreted, either unchanged or metabolized, and are discharged to the environment through animal manure, municipal wastewater or biosolids. Consequently, these chemicals reach cropland, which is advocated as a means of recycling. As these drugs are used in escalating quantities, there is growing concern over their presence, toxicity and fate in the soil, which may pose adverse effects on plant growth and productivity, as well as result in their uptake and accumulation in crops. These will contaminate the food chain and eventually affect human health. In this review, we summarize recent research and provide a detailed overview of antibiotics in soil-plant systems, including 1) the occurrence and determination of antibiotics around the world and their routes of entry to the environment, 2) the impact of wastewater irrigation and animal manure or biosolids amendment on agricultural soils, 3) the transport and persistence of antibiotics in the terrestrial environment, and 4) the bioaccumulation and translocation of antibiotics in different tissues of edible crops under laboratory and field conditions. Their impacts on the environment and potential human exposure are elucidated. Knowledge gaps and future research perspectives are discussed.

Leaching behavior of veterinary antibiotics in animal manure-applied soils.

Agricultural fields worldwide are being contaminated by the escalating application of veterinary antibiotics (VAs) via animal manure and biosolids applied as fertilizers or of wastewater for irrigation, resulting in soil degradation and damage to the health of terrestrial environments. This paper describes a series of column studies investigating the leaching behavior of five VAs, tetracycline (TC), sulfamethazine (SMZ), norfloxacin (NOR), erythromycin (ERY) and chloramphenicol (CAP), under different simulated rainfall conditions that could occur in agricultural environments. Our aim was to explore the effects of acid rain and torrential rain on the leaching of different VAs and to determine their leaching behaviors along the soil profile. The results showed that acid rain accelerated the accumulation of VAs from animal manure in surface soil while long rainfall durations promoted the downward migration of VAs in soil. Under acid rain conditions, a higher concentration of VAs remained in the animal manure. More VAs were eluted to deeper soil layers and the leachate under extreme rainfall conditions. The leachability of VAs was higher in sandy soil than in clay or loamy soil. SMZ and ERY posed a higher risk to deeper soil layers and groundwater, while NOR and TC tended to persist in surface soil, which can be explained by their different physicochemical properties in soil. Moreover, the general trends from two model assessments and soil column measurements appeared to be in agreement. SMZ had a high leachability, while NOR tended to accumulate in soils. This study provided vital insight into the persistence mechanisms of VAs in terrestrial environments and their potential risks to soils and groundwater.

Phytotoxicity of veterinary antibiotics to seed germination and root elongation of crops.

Large quantities of veterinary antibiotics (VAs) are being used worldwide in agricultural fields through wastewater irrigation and manure application. They cause damages to the ecosystem when discharged into the environment, but there is a lack of information on their toxicity to plants and animals. This study evaluated the phytotoxic effects of five major VAs, namely tetracycline (TC), sulfamethazine (SMZ), norfloxacin (NOR), erythromycin (ERY) and chloramphenicol (CAP), on seed germination and root elongation in lettuce, tomato, carrot and cucumber, and investigated the relationship between their physicochemical properties and phytotoxicities. Results show that these compounds significantly inhibited root elongation (p<0.05), the most sensitive endpoint for the phytotoxicity test. TC was associated with the highest level of toxicity, followed by NOR, ERY, SMZ and CAP. Regarding crop species, lettuce was found to be sensitive to most of the VAs. The median effect concentration (EC50) of TC, SMZ, NOR, ERY and CAP to lettuce was 14.4, 157, 49.4, 68.8 and 204 mg/L, respectively. A quantitative structure-activity relationship (QSAR) model has been established based on the measured data. It is evident that hydrophobicity was the most important factor governing the phytotoxicity of these compounds to seeds, which could be explained by the polar narcosis mechanism. Lettuce is considered a good biomarker for VAs in the environment. According to the derived equation, phytotoxicities of selected VA compounds on different crops can be calculated, which could be applicable to other VAs. Environmental risks of VAs were summarized based on the phytotoxicity results and other persistent factors.

Adsorption and degradation of five selected antibiotics in agricultural soil.

Large quantities of antibiotics are being added to agricultural fields worldwide through the application of wastewater, manures and biosolids, resulting in antibiotic contamination and elevated environmental risks in terrestrial environments. Most studies on the environmental fate of antibiotics focus on aquatic environments or wastewater treatment plants. Little is known about the behavior of antibiotics at environmentally relevant concentrations in agricultural soil. In this study we evaluated the adsorption and degradation of five different antibiotics (tetracycline, sulfamethazine, norfloxacin, erythromycin, and chloramphenicol) in sterilized and non-sterilized agricultural soils under aerobic and anaerobic conditions. Adsorption was highest for tetracycline (Kd, 1093 L/kg), while that for sulfamethazine was negligible (Kd, 1.365 L/kg). All five antibiotics were susceptible to microbial degradation under aerobic conditions, with half-lives ranging from 2.9 to 43.3 d in non-sterilized soil and 40.8 to 86.6 d in sterilized soil. Degradation occurred at a higher rate under aerobic conditions but was relatively persistent under anaerobic conditions. For all the antibiotics, a higher initial concentration was found to slow down degradation and prolong persistence in soil. The degradation behavior of the antibiotics varied in relation to their physicochemical properties as well as the microbial activities and aeration of the recipient soil. The poor adsorption and relative persistence of sulfamethazine under both aerobic and anaerobic conditions suggest that it may pose a higher risk to groundwater quality. An equation was proposed to predict the fate of antibiotics in soil under different field conditions, and assess their risks to the environment.

Distribution of antibiotics in wastewater-irrigated soils and their accumulation in vegetable crops in the Pearl River Delta, southern China.

Wastewater is increasingly being used to irrigate agricultural land in many countries around the world. However, limited research has examined the occurrence of antibiotics in soil irrigated with wastewater and their accumulation in plants. This study aimed to determine the distribution of various types of antibiotics in different environmental matrices in the Pearl River Delta (PRD) region and to evaluate their accumulation and translocation in edible crops. Samples were collected from six sites in the PRD where either domestic wastewater or fishpond water was used for irrigation. Results showed that fishpond water irrigated soils had higher concentrations of antibiotics than wastewater-irrigated soils. Different trends were observed in the accumulation of antibiotics in the different edible parts of various crops. Despite the low human annual exposure to antibiotics through the consumption of edible crops (1.10 to 7950 µg/y), the potential adverse effects of antibiotics along the food chain should not be neglected.

Carbon emission and sequestration of urban turfgrass systems in Hong Kong.

Climate change is more than just a global issue. Locally released carbon dioxide may lead to a rise in global ambient temperature and influence the surrounding climate. Urban greenery may mitigate this as they can remove carbon dioxide by storing carbon in substrates and vegetation. On the other hand, urban greenery systems which are under intense management and maintenance may contribute to the emission of carbon dioxide or other greenhouse gases. The impact of urban greenery on carbon balance in major metropolitan areas thus remains controversial. We investigated the carbon footprints of urban turf operation and maintenance by conducting a research questionnaire on different Hong Kong turfs in 2012, and showed that turf maintenance contributed 0.17 to 0.63 kg Ce m(-2)y(-1) to carbon emissions. We also determined the carbon storage of turfs at 0.05 to 0.21 kg C m(-2) for aboveground grass biomass and 1.26 to 4.89 kg C m(-2) for soils (to 15 cm depth). We estimated that the carbon sink capacity of turfs could be offset by carbon emissions in 5-24 years under current management patterns, shifting from carbon sink to carbon source. Our study suggested that maintenance management played a key role in the carbon budget and footprint of urban greeneries. The environmental impact of turfgrass systems can be optimized by shifting away from empirically designed maintenance schedules towards rational ones based on carbon sink and emission principles.

Fate and distribution of nitrogen in soil and plants irrigated with landfill leachate.

Landfill leachate contains a high concentration of ammoniacal substances which can be a potential supply of N for plants. A bioassay was conducted using seeds of Brassica chinensis and Lolium perenne to evaluate the phytotoxicity of the leachate sample. A soil column experiment was then carried out in a greenhouse to study the effect of leachate on plant growth. Two grasses (Paspalum notatum and Vetiver zizanioides) and two trees (Hibiscus tiliaceus and Litsea glutinosa) were irrigated with leachate at the EC50 levels for 12 weeks. Their growth performance and the distribution of N were examined and compared with columns applied with chemical fertilizer. With the exception of P. notatum, plants receiving leachate and fertilizer grew better than those receiving water alone. The growth of L. glutinosa and V. zizanioides with leachate irrigation did not differ significantly from plants treated with fertilizer. Leachate irrigation significantly increased the levels of NH(x)-N in soil. Although NO(x)-N was below 1 mg NL(-1) in the leachate sample, the soil NO(x)-N content increased by 9-fold after leachate irrigation, possibly as a result of nitrification. Leachate irrigation at EC50 provided an N input of 1920 kg N ha(-1) over the experimental period, during which up to 1050 kg N ha(-1) was retained in the soil and biomass, depending on the type of vegetation. The amount of nutrient added seems to exceed beyond the assimilative capability. Practitioners should be aware of the possible consequence of N saturation when deciding the application rate if leachate irrigation is aimed for water reuse.

Environmental fate and non-target impact of glyphosate-based herbicide (Roundup) in a subtropical wetland.

Mai Po Nature Reserve (Hong Kong) is an internationally important wetland for waterbirds. Roundup, a formulation based on glyphosate, has been used to control the widespread weeds within the reserve for many years but the fate and non-target impact of the herbicide is unknown. To fill this knowledge gap, we applied Roundup by hand-held sprayer to an estuarine and a freshwater pond in the dry season of year 2002. The surface water and sediment were sampled routinely for glyphosate concentrations following one month of application. In situ bioassays using local edible fish species were performed along with the herbicide application. Up to 52% of glyphosate in the surface water was transported to the unapplied regions by wind-driven current in the estuarine pond at 1 DPT (day post treatment). For both ponds, glyphosate concentrations in the water decreased rapidly after 1-3 DPT, but then decreased gradually over time. Both physical adsorption to the bottom sediments and microbial degradation are thought to contribute to these decreases. Interestingly, the persistence of glyphosate in the freshwater pond was longer than in the estuarine system, which is likely due to the considerably higher concentrations of chelating metals (i.e. Cu and Fe) present in the sediment (4.5 and 11-fold higher, respectively) which potentially reduced the bioavailability of glyphosate to the microbial decomposers. Lastly, fishes used in the in situ bioassays (both in applied and unapplied areas) showed similar survival rates, indicating that the use of Roundup at the provided application rate posed no serious hazard.

Phytotoxicity data safeguard the performance of the recipient plants in leachate irrigation.

Leachates from an operating and a closed landfill were examined for their phytotoxicity by seed germination/root elongation tests using seeds of Brassica chinensis and Lolium perenne. Their EC50s ranged from 3% to 46% v/v, which varied remarkably with the operating status of the landfills. Seedlings of twelve tree species were grown in pots, which were irrigated with landfill leachate at the EC50 levels, with tap water as control. No tree mortality or growth inhibition was observed after 90 days of leachate application. Chlorophyll fluorescence measurement also showed that plants receiving leachate did not suffer from a decline in photosynthetic efficiency. Litsea glutinosa and Hibiscus tiliaceus had remarkable growth, and other non-N-fixers were not inferior to the N-fixing Acacia auriculiformis. Leachate irrigation improved soil N content, though P deficiency is still a problem. The seed bioassay provided a conservative estimate of the phytotoxicity of landfill leachate. Plants irrigated can be protected from growth inhibition when the leachate irrigation plan is designed with reference to phytotoxicity data.

Influence of glyphosate and its formulation (Roundup) on the toxicity and bioavailability of metals to Ceriodaphnia dubia.

This study examined the toxicological interaction between glyphosate (or its formulation, Roundup) and several heavy metals to a freshwater cladoceran, Ceriodaphnia dubia. We demonstrated that all binary combinations of Roundup and metals (Cd, Cu, Cr, Ni, Pb, Se and Zn) exhibited "less than additive" mixture toxicity, with 48-h LC50 toxic unit > 1. Addition of glyphosate alone could significantly reduce the acute toxicity of Ag, Cd, Cr, Cu, Ni, Pb and Zn (but not Hg and Se). The ratio between glyphosate and metal ions was important in determining the mitigation of metal toxicity by glyphosate. A bioaccumulation study showed that in the presence of glyphosate the uptake of some metals (e.g. Ag) was halted but that of others (e.g. Hg) was increased significantly. Therefore, our study strongly suggests that glyphosate and its commercial formulations can control the toxicity as well as the bioavailability of heavy metals in aquatic ecosystems where both groups of chemicals can co-occur.

Comparative toxicity of glyphosate-based herbicides: aqueous and sediment porewater exposures.

Glyphosate-based herbicides are widely used for aquatic weed control. However, their aquatic toxicity data, especially those on sediment, are relatively scarce. In this study, the water-only acute toxicity of three formulations based on glyphosate (Rodeo, Roundup Biactive, and Roundup) were compared using a water-column organism (cladoceran: Ceriodaphnia dubia) and a benthic organism (amphipod: Hyalella azteca). In addition, Roundup Biactive and Roundup were spiked into a clean sediment which was amended with appropriate amounts of peat moss to study the effect of different organic carbon levels (0, 0.4, 1.2, and 2.1%) on their sediment toxicity, with C. dubia exposed to overlying water or porewater prepared from the contaminated sediments. Results showed that the toxicity based on 48-h LC50s for the three herbicides in the water-only tests was Roundup (1.5-5.7 mg L(-1)) > Roundup Biactive (82-120 mg L(-1)) > Rodeo (225-415 mg L(-1)), and H. azteca was generally more sensitive than C. dubia to these herbicides. Toxicity differences between formulations were due to the different surfactant components in these herbicides. From the porewater toxicity tests, Roundup Biactive (340 mg kg(-1)) and Roundup (244 mg kg(-1)) were similarly toxic in the sediment tests at 0% organic carbon, indicating that the surfactants in Roundup were considerably more adsorptive than those in Roundup Biactive to the sediment of the same organic carbon. Also, an increase in organic carbon significantly decreased the toxicity of Roundup in sediment, but not for Roundup Biactive. Sediment-porewater partitioning of glyphosate was found to be influenced by sediment organic carbon (i.e., glyphosate adsorption increased with sediment organic carbon).

Microbial enhancement of Cu2+ removal capacity of Eichhornia crassipes (Mart.).

Bacteria resistant to Cu2+, Ni2+ or Zn2+ were isolated from the rhizosphere of water hyacinth (Eichhornia crassipes (Mart.)) and their metal ion removal capacities (RCs) were determined. The Ni2+ and Zn2+ RCs of the respective metal ion-resistant bacteria were less than 4.1 mg g(-1), while one of the Cu2+-resistant bacteria (Strain CU-1) showed a significant high Cu2+ RC of 10.6 mg g(-1). The effect of inoculating water hyacinth with Strain CU-1 on its Cu2+ RC was further studied. Water hyacinths were treated with an antibiotic, oxytetracycline (OTC), to remove most rhizospheric bacteria of plant roots. Inoculation of Strain CU-1 increased the Cu2+ RC of the plant root by 1.91 (OTC-treated) and 1.56 (OTC-untreated) folds respectively when compared with the control. Results also showed that Strain CU-1 colonized onto the plant root and led to the increase of Cu2+ RC of the roots of water hyacinth.

Aquatic toxicity of glyphosate-based formulations: comparison between different organisms and the effects of environmental factors.

Glyphosate-based herbicides (e.g. Roundup) are extensively used in the aquatic environment, but there is a paucity of data on the toxicity of the formulated products and the influences by environmental factors. In this study, the acute toxicity of technical-grade glyphosate acid, isopropylamine (IPA) salt of glyphosate, Roundup and its surfactant polyoxyethylene amine (POEA) to Microtox bacterium (Vibrio fischeri), microalgae (Selenastrum capricornutum and Skeletonema costatum), protozoa (Tetrahymena pyriformis and Euplotes vannus) and crustaceans (Ceriodaphnia dubia and Acartia tonsa) was examined and the relative toxicity contributions of POEA to Roundup were calculated. The effects of four environmental factors (temperature, pH, suspended sediment and algal food concentrations) on the acute toxicity of Roundup to C. dubia were also examined. Generally, the toxicity order of the chemicals was: POEA>Roundup>glyphosate acid>IPA salt of glyphosate, while the toxicity of glyphosate acid was mainly due to its high acidity. Microtox bacterium and protozoa had similar sensitivities towards Roundup toxicity (i.e. IC50 from 23.5 to 29.5 mg AE/l). In contrast, microalgae and crustaceans were 4-5 folds more sensitive to Roundup toxicity than bacteria and protozoa. Except photosynthetic microalgae, POEA accounted for more than 86% of Roundup toxicity and the toxicity contribution of POEA was shown to be species-dependent. Increase in pH (6-9) and increase of suspended sediment concentration (0-200 mg/l) significantly increased the toxicity of Roundup to C. dubia, but there were no significant effects due to temperature change and food addition.

Effects of leachate recirculation on biogas production from landfill co-disposal of municipal solid waste, sewage sludge and marine sediment.

Leachate recirculation is an emerging technology associated with the management of landfill. The impact of leachate recirculation on the co-disposal of three major wastes (municipal solid waste, sewage sludge and sediment dredgings) was investigated using a laboratory column study. Chemical parameters (pH, COD, ammoniacal-N, total-P) and gas production (total gas volume, production rates and concentrations of CH4 and CO2) were monitored for 11 weeks. Leachate recirculation reduced waste-stabilization time and was effective in enhancing gas production and improving leachate quality, especially in terms of COD. The results also indicated that leachate recirculation could maximize the efficiency and waste volume reduction rate of landfill sites.