Aquatic toxicity of triclosan

The aquatic toxicity of triclosan (TCS), a chlorinated biphenyl ether used as an antimicrobial in consumer products, was studied with activated-sludge microorganisms, algae, invertebrates, and fish. Triclosan, a compound used for inhibiting microbial growth, was not toxic to wastewater microorganisms at concentrations less than aqueous solubility. The 48-h Daphnia magna median effective concentration (EC50) was 390 microg/L and the 96-h median lethal concentration values for Pimephales promelas and Lepomis macrochirus were 260 and 370 microg/L, respectively. A no-observed-effect concentration (NOEC) and lowest-observed-effect concentration of 34.1 microg/L and 71.3 microg/L, respectively, were determined with an early life-stage toxicity test with Oncorhynchus mykiss. During a 96-h Scenedesmus study, the 96-h biomass EC50 was 1.4 microg/L and the 96-h NOEC was 0.69 microg/L. Other algae and Lemna also were investigated. Bioconcentration was assessed with Danio rerio. The average TCS accumulation factor over the five-week test period was 4,157 at 3 microg/L and 2,532 at 30 microg/L. Algae were determined to be the most susceptible organisms. Toxicity of a TCS-containing wastewater secondary effluent to P. promelas and Ceriodaphnia was evaluated and no observed differences in toxicity between control and TCS-treated laboratory units were detected. The neutral form of TCS was determined to be associated with toxic effects. Ionization and sorption will mitigate those effects in the aquatic compartment.     

Activity and population dynamics of heterotrophic and ammonia-oxidizing microorganisms in soil surrounding sludge bands spiked with linear alkylbenzene sulfonate: a field study

Recent research has documented soil microorganisms to be rather sensitive to linear alkylbenzene sulfonates (LAS), which may enter the soil environment in considerable quantities following sewage sludge disposal. We here report field effects of LAS on selected microbial populations present in a sandy soil surrounding well-defined sludge bands spiked with high but realistic LAS levels (7.1 or 31.3 g/kg). Surprisingly, LAS had no effect on heterotrophic respiration in the sludge compartment per se but stimulated activity and metabolic quotient (microbial activity per unit of biomass) in the surrounding soil. By contrast, autotrophic ammonia oxidation was initially inhibited in the LAS-spiked sludge. This led to dramatic transient increases of NH4+ availability in the sludge and surrounding soil, subsequently stimulating soil ammonia oxidizers. As judged from a Nitrosomonas europaea bioluminescence toxicity assay, however, LAS or other sludge components never accumulated to toxic levels in the soil compartments and the LAS tolerance of the indigenous microbes further remained unchanged following LAS exposure. LAS effects on the investigated microbial populations largely occurred during the first two months and were confined to soil closer than 30 mm from LAS-spiked sludge. Our results strongly suggest that disposal of LAS-contaminated sludge does not pose a major risk to the function of the soil microbial community under field conditions.     

Toxicity of Organotin Compounds to Activated Sludge

Inhibition of respiration rate of activated sludge heterotrophic microorganisms was determined for tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT), and triphenyltin (TPhT). TBT, DBT, and TPhT exhibit similar acute toxicity to activated sludge, while MBT is less toxic. The effect of various experimental parameters, such as sludge age, concentrations of suspended solids, and exposure time, on toxicity was investigated. An increase in sludge age or in the concentration of suspended solids reduces the observed inibition. Longer exposure seems to increase the inhibition of TBT, DBT, and TPhT during the first hours of exposure, while later the inhibition remains constant. In the case of MBT, 24 h after exposure, the respiration rate was similar to that of the control biomass.     

Fate and effects of triclosan in activated sludge

Triclosan (TCS; 5-chloro-2-[2,4-dichloro-phenoxy]-phenol) is a widely used antimicrobial agent. To understand its fate during sewage treatment, the biodegradation and removal of TCS were determined in activated sludge. In addition, the effects of TCS on treatment processes were assessed. Fate was determined by examining the biodegradation and removal of TCS radiolabeled with 14C in the 2,4-dichlorphenoxy ring in laboratory batch mineralization experiments and bench-top continuous activated-sludge (CAS) systems. In batch experiments with unacclimated sludge, TCS was mineralized to 14CO2, but the total yield varied as a function of test concentration. Systems that were redosed with TCS exhibited more extensive and faster mineralization, indicating that adaptation was a critical factor determining the rate and extent of biodegradation. In a CAS study in which the influent level of TCS was incrementally increased from 40 microg/L to 2,000 microg/L, removal of the parent compound exceeded 98.5% and removal of total radioactivity (parent and metabolites) exceeded 85%. Between 1.5 and 4.5% of TCS in the influent was sorbed to the wasted solids, whereas >94% underwent primary biodegradation and 81 to 92% was mineralized to CO2 or incorporated in biomass. Increasing levels of TCS in the influent had no major adverse effects on any wastewater treatment process, including chemical oxygen demand, biological oxygen demand, and ammonia removal. In a subsequent experiment, a CAS system, acclimated to TCS at 35 microg/L, received two separate 4-h shock loads of 750 microg/L TCS. Neither removal of TCS nor treatment processes exhibited major adverse effects. An additional CAS study was conducted to examine the removal of a low level (10 microg/L) of TCS. Removal of parent equaled 94.7%, and biodegradation remained the dominant removal mechanism. A subsequent series of CAS experiments examined removal at four influent concentrations (7.5, 11, 20, and 50 microg/L) of TCS and demonstrated that removal of parent ranged from 98.2 to 99.3% and was independent of concentration. Although TCS removal across all experiments appeared unrelated to influent concentration, removal was significantly correlated (r2 = 0.87) with chemical oxygen demand removal, indicating that TCS removal was related to overall treatment efficiency of specific CAS units. In conclusion, the experiments show that TCS is extensively biodegraded and removed in activated-sludge systems and is unlikely to upset sewage treatment processes at levels expected in household and manufacturing wastewaters.     

Effects of chloramphenicol, florfenicol, and thiamphenicol on growth of algae Chlorella pyrenoidosa, Isochrysis galbana, and Tetraselmis chui

This study investigated the growth inhibition effects of three phenicol antibiotics on microalgae used in aquaculture. Different dose levels of chloramphenicol (CAP), florfenicol (FF), and thiamphenicol (TAP) were added to cultures of one freshwater green alga, Chlorella pyrenoidosa, and two marine algae, Isochrysis galbana and Tetraselmis chui. For the two marine algae, FF showed higher toxicity levels (EC50, 1.3-8 mg l(-1)) than CAP (4-41 mg l(-1)) and TAP (38-158 mg l(-1)). CAP was more toxic to the freshwater algae (EC50, 14 mg l(-1)) than FF (215 mg l(-1)) and TAP (1283 mg l(-1)). TAP was the least toxic to the three algae, but maintained the highest stability during the test period. Among the tested algae, T. chui was the species most sensitive to the three antibiotics. This study demonstrates that all three phenicol antibiotics can inhibit growth of the three microalgae and should be carefully used in aquaculture.     

Assessment of lead toxicity to the marine bacterium, Vibrio fischeri, and to a heterogeneous population of microorganisms derived from the Pearl River in Jackson, Mississippi, USA.

Microorganisms are known to be excellent test organisms because of the relative ease for handling and suitability for analysis related to their small size, large number and convenient growing conditions. In this research, we tested the toxic effects of lead against a marine bacterium (Vibrio fischeri), and a heterogeneous population of bacteria derived from the Pearl River in Jackson, Mississippi. Using the level of bioluminescence in the Microtox Assay (V. fischeri), and the kinetics of dissolved oxygen uptake and growth (mixed bacterial population) as measures of toxicity, lead concentrations effecting a 50% reduction in these parameters (EC50) were determined as the toxic end-points. The activity quotients were also computed to determine the degrees of toxicity. Optical density (measure of growth) and oxygen uptake were measured over an extended period of time (20 h). EC50 values of 0.34 +/- 0.03, 3.10 +/- 0.01, and 3.80 +/- 0.02 mg/L were recorded for bioluminescence, growth, and oxygen uptake, respectively. As expected, the results indicated that the sensitivity to lead toxicity of V. fischeri was about one order of magnitude (10 times) greater than that of the mixed population of Pearl River microorganisms. Reductions in bioluminescence, growth, and oxygen uptake were directly correlated to lead concentrations, with toxic levels ranging from slightly toxic in lower concentrations to extremely toxic in higher concentrations. Upon 20 h of exposure, the times required to produce 50% reduction in dissolved oxygen uptake were (TD50S) 8.01 +/- 0.44, 9.60 +/- 0.46, 11.29 +/- 0.46, 13.03 +/- 0.57, 17.32 +/- 0.95, and 20.00 +/- 0.00 h in 0, 1, 2, 3, 4, 5, and 6 mg/L of lead, respectively, indicating a time-response relationship with respect to lead toxicity.     

Toxicity of Ammonia Nitrogen to Ciliated Protozoa <Emphasis Type="Italic">Stentor coeruleus</Emphasis> and <Emphasis Type="Italic">Coleps hirtus</Emphasis> Isolated from Activated Sludge of Wastewater Treatment Plants

We assessed the toxicity of ammonia ions to Stentor coeruleus and Coleps hirtus (Protozoa) isolated from activated sludge taken from two municipal wastewater treatment plants in southern Poland. Stentor coeruleus is a rarely occurring species in activated sludge, unlike the widespread Coleps hirtus. The mean LC50 values (concentration causing 50 % mortality) calculated for the 24 h tests differed hugely between the tested species: 43.03 mg NH⁴⁺ dm⁻³ for Stentor coeruleus and 441.12 mg NH⁴⁺ dm⁻³ for Coleps hirtus. The ammonia ion concentration apparently is an important factor in the occurrence of these protozoan species in activated sludge.     

Ecotoxicological characterization of hazardous wastes

In Europe hazardous wastes are classified by 14 criteria including ecotoxicity (H 14). Standardized methods originally developed for chemical and soil testing were adapted for the ecotoxicological characterization of wastes including leachate and solid phase tests. A consensus on which tests should be recommended as mandatory is still missing. Up to now, only a guidance on how to proceed with the preparation of waste materials has been standardized by CEN as EN 14735. In this study, tests including higher plants, earthworms, collembolans, microorganisms, duckweed and luminescent bacteria were selected to characterize the ecotoxicological potential of a boiler slag, a dried sewage sludge, a thin sludge and a waste petrol. In general, the instructions given in EN 14735 were suitable for all wastes used. The evaluation of the different test systems by determining the LC/EC₅₀ or NOEC-values revealed that the collembolan reproduction and the duckweed frond numbers were the most sensitive endpoints. For a final classification and ranking of wastes the Toxicity Classification System (TCS) using EC/LC₅₀ values seems to be appropriate.     

Toxicity and bioaccumulation of biosolids-borne triclosan in terrestrial organisms

Triclosan (TCS) is a common constituent of personal care products and is frequently present in biosolids. Application of biosolids to land transfers significant amounts of TCS to soils. Because TCS is an antimicrobial and is toxic to some aquatic organisms, concern has arisen that TCS may adversely affect soil organisms. The objective of the present study was to investigate the toxicity and bioaccumulation potential of biosolids-borne TCS in terrestrial micro- and macro-organisms (earthworms). Studies were conducted in two biosolids-amended soils (sand, silty clay loam), following U.S. Environmental Protection Agency (U.S. EPA) guidelines. At the concentrations tested herein, microbial toxicity tests suggested no adverse effects of TCS on microbial respiration, ammonification, and nitrification. The no observed effect concentration for TCS for microbial processes was 10?mg/kg soil. Earthworm subchronic toxicity tests showed that biosolids-borne TCS was not toxic to earthworms at the concentrations tested herein. The estimated TCS earthworm lethal concentration (LC50) was greater than 1?mg/kg soil. Greater TCS accumulation was observed in earthworms incubated in a silty clay loam soil (bioaccumulation factor [BAF]?=?12?±?3.1) than in a sand (BAF?=?6.5?±?0.84). Field-collected earthworms had a significantly smaller BAF value (4.3?±?0.7) than our laboratory values (6.5-12.0). The BAF values varied significantly with exposure conditions (e.g., soil characteristics, laboratory vs field conditions); however, a value of 10 represents a reasonable first approximation for risk assessment purposes.     

Effects and risk assessment of linear alkylbenzene sulfonates in agricultural soil. 2. Effects on soil microbiology as influenced by sewage sludge and incubation time

The anionic surfactant linear alkylbenzene sulfonate (LAS) may inhibit soil microorganisms and may occur in agricultural soil through the application of sewage sludge. For five microbial parameters (microbial biomass C and the potentials of iron reduction, ammonium oxidation, dehydrogenase activity, and arylsulfatase activity), we compared the effects of aqueous LAS and LAS-spiked sewage sludge added to existing levels of 0, 3, 8, 22, 22, 62, 174, and 488 mg/kg soil (dry wt) in a Danish sandy agricultural soil that was incubated for 5 d to eight weeks. Arylsulfatase activity (measured after four weeks of incubation) was rather insensitive to LAS, with an EC 10 of 222 and more than 488 mg/kg in soil samples treated with aqueous LAS and LAS-spiked sewage sludge, respectively. For the other microbial parameters, the short-term effects (approximately one to two weeks) of aqueous LAS were characterized by an EC10 in the range of 3 to 39 mg/kg. Application of LAS via sewage sludge generally reduced the short-term effects for the microbial parameters, and the EC10 for LAS in sludge-amended soil after approximately one to two weeks of incubation ranged from less than 8 to 102 mg/kg. Recovery potential was seen for most microbial parameters as a result of prolonged incubation, both under conditions of LAS persistence (anaerobic conditions, the iron-reduction test) and LAS depletion (aerobic incubations, all other assays). In conclusion, the short-term inhibitory effects of LAS on soil microbiology were decreased in the presence of sewage sludge and by a prolonged (two to eight weeks) laboratory incubation period.     

Assessing the Toxicity of Chemical Compounds Associated With Land-Based Marine Fish Farms: The Sea Urchin Embryo Bioassay With Paracentrotus lividus and Arbacia lixula

In aquaculture, disinfection of facilities, prevention of fish diseases, and stimulation of fish growth are priority goals and the most important sources of toxic substances to the environment, together with excretory products from fish. In the present study, embryos of two species of sea urchin (Paracentrotus lividus and Arbacia lixula) were exposed to serial dilutions of six antibiotics (amoxicillin (AMOX), ampicillin, flumequine (FLU), oxytetracycline (OTC), streptomycin (ST), and sulfadiazine [SFD]) and two disinfectants (sodium hypochlorite (NaClO) and formaldehyde [CH(2)O]). Alterations in larval development were studied, and the effective concentrations (ECs) were calculated to evaluate the toxicity of the substances. Both species showed similar sensitivities to all substances tested. Disinfectants (EC(50) = 1.78 and 1.79 mg/l for CH(2)O; EC(50) = 10.15 and 11.1 mg/l for NaClO) were found to be more toxic than antibiotics. AMOX, OTC, and ST caused <20 % of alterations, even at the highest concentrations tested. FLU was the most toxic to P. lividus (EC(50) = 31.0 mg/l) and SFD to A. lixula (EC(50) = 12.7 mg/l). The sea urchin bioassay should be considered within toxicity assessment-monitoring plans because of the sensitivity of larvae to disinfectants.     

Long-Term Effects of Antibiotics on the Elimination of Chemical Oxygen Demand, Nitrification, and Viable Bacteria in Laboratory-Scale Wastewater Treatment Plants

Antibiotics and other pharmaceuticals are contaminants of the environment because of their widespread use and incomplete removal by microorganisms during wastewater treatment. The influence of a mixture of ciprofloxacin (CIP), gentamicin (GM), sulfamethoxazole (SMZ)/trimethoprim (TMP), and vancomycin (VA), up to a final concentration of 40?mg/L, on the elimination of chemical oxygen demand (COD), nitrification, and survival of bacteria, as well as the elimination of the antibiotics, was assessed in a long-term study in laboratory treatment plants (LTPs). In the presence of 30?mg/L antibiotics, nitrification of artificial sewage by activated sludge ended at nitrite. Nitrate formation was almost completely inhibited. No nitrification at all was possible in the presence of 40?mg/L antibiotics. The nitrifiers were more sensitive to antibiotics than heterotrophic bacteria. COD elimination in antibiotic-stressed LTPs was not influenced by?≤20?mg/L antibiotics. Addition of 30?mg/L antibiotic mixture decreased COD removal efficiency for a period, but the LTPs recovered. Similar results were obtained with 40?mg/L antibiotic mixture. The total viable count of bacteria was not affected negatively by the antibiotics. It ranged from 2.2?×?10(6) to 8.2?×?10(6) colony-forming units per milliliter (CFU/mL) compared with the control at 1.4?×?10(6)-6.3?×?10(6) CFU/mL. Elimination of the four antibiotics during phases of 2.4-30?mg/L from the liquid was high for GM (70-90?%), much lower for VA, TMP, and CIP (0-50?%), and highly fluctuating for SMZ (0-95?%). The antibiotics were mainly adsorbed to the sludge and not biodegraded.     

Measurement of triclosan in wastewater treatment systems

The objective of this study was to investigate the fate and removal of triclosan (TCS; 5-chloro-2-[2,4-dichloro-phenoxy]-phenol), an antimicrobial agent used in a variety of household and personal-care products, in wastewater treatment systems. This objective was accomplished by monitoring the environmental concentrations of TCS, higher chlorinated derivatives of TCS (4,5-dichloro-2-[2,4-dichloro-phenoxy]-phenol [tetra II]; 5,6-dichloro-2-[2,4-dichloro-phenoxy]-phenol [tetra III]; and 4,5,6-trichloro-2-(2,4-dichloro-phenoxy)-phenol [penta]), and a potential biotransformation by-product of TCS (5-chloro-2-[2,4-dicholoro-phenoxy]-anisole [TCS-OMe]) during wastewater treatment. These analytes were isolated from wastewater by using a C18 solid-phase extraction column and from sludge with supercritical fluid CO2. Once the analytes were isolated, they were derivatized to form trimethylsilylethers before quantitation by gas chromatography-mass spectrometry. Recovery of TCS from laboratory-spiked wastewater samples ranged from 79 to 88% for influent, 36 to 87% for final effluent, and 70 to 109% for primary sludge. Field concentrations of TCS in influent wastewater ranged from 3.8 to 16.6 microg/L and concentrations for final effluent ranged from 0.2 to 2.7 microg/L. Removal of TCS by activated-sludge treatment was approximately 96%, whereas removal by trickling-filter treatment ranged from 58 to 86%. The higher chlorinated tetra-II, tetra-III, and penta closans were below quantitation in all of the final effluent samples, except for one sampling event. Digested sludge concentrations of TCS ranged from 0.5 to 15.6 microg/g (dry wt), where the lowest value was from an aerobic digestion process and the highest value was from an anaerobic digestion process. Analysis of these results suggests that TCS is readily biodegradable under aerobic conditions, but not under anaerobic conditions. The higher chlorinated closans were near or below the limit of quantitation in all of the digested sludge samples. Based on results from this study, the chlorinated analogues and biotransformation by-product of TCS are expected to be very low in receiving waters and sludge-amended soils.     

Synthesis and leishmanicidal activities of 1-(4-X-phenyl)-N'-[(4-Y-phenyl)methylene]-1H-pyrazole-4-carbohydrazides

1H-pyrazole-4-carbohydrazides were synthesized and their leishmanicidal in vitro activities and cytotoxic effects were investigated. The drugs prototypes of these new compounds (ketoconazole, benznidazole, allopurinol and pentamidine) were also tested. It was found that among all the 1H-pyrazole-4-carbohydrazides derivatives examined, the most active compounds were those with X = Br, Y = NO2 (27) and X = NO2, Y = Cl (15) derivatives which showed to be most effective on promastigotes forms of L. amazonensis than on L. chagasi and L. braziliensis species. When tested against murine peritoneal macrophages as mammalian host cell controls of toxicity, 1-(4-Br-phenyl)-N'-[(4-NO(2)-phenyl)methylene]-1H-pyrazole-4-carbohydrazides (27) (EC50 = 50 microM l(-1)) and 1-(4-NO2-phenyl)-N'-[(4-Cl-phenyl)methylene]-1H-pyrazole-4-carbohydrazides (15) EC50 = 80 microM l(-1))] was reasonably toxic. However, both compounds were less toxic than pentamidine and ketoconazole. These results provide new perspectives on the development of drugs with activities against Leishmania parasite.     

Biodegradability assessment of ozonated raw and biotreated pharmaceutical wastewater

The activated sludge specific oxygen uptake rate (SOUR) and BOD₅/COD ratios of biologically pretreated pharmaceutical wastewater were analyzed and compared to assess relative changes in biotreatability during ozonation at a rate of 7.4 g/(L × h) for 4 h. An appreciable COD removal (41%) was achieved by the initial biological treatment process, whereas ozonation was more effective in reducing the UV-sensitive aromatic compounds present in the pretreated effluent. Sequential treatment using activated sludge + ozonation processes resulted in an average COD removal efficiency of 48%, and a proceeding biotreatment stage increased the overall COD removal to 53%. An optimum ozone dose in the range of 1,854–3,708 mg/L corresponding to a specific ozone input rate of 0.23–0.46 mg O₃/mg COD_o existed where SOUR (3.7 × 10⁻³ mg O₂/[mg MLSS × min] for ozonation at pH 8) and BOD₅/COD (0.57) as well as the proceeding biological COD removal yield Y _COD (average 8 mg COD/mg MLSS) exerted maximum values. Received: 24 November 2001/Accepted: 25 April 2002     

Ecotoxicity and genotoxicity assessment of cytostatic pharmaceuticals

The fate and effects of cytostatic (anticancer or antineoplastic) pharmaceuticals in the environment are largely unknown, but they can contaminate wastewater treatment effluents and consequently aquatic ecosystems. In this paper, we have focused on five cytostatic compounds used in high amounts (cyclophosphamide, cisplatin, 5-fluorouracil, doxorubicin, and etoposide), and we have investigated their ecotoxicity in bacterial Pseudomonas putida growth-inhibition test, algal Pseudokirchneriella subcapitata growth-inhibition test, and Dapnia magna acute immobilization test. Genotoxicity also was assessed with Escherichia coli SOS-chromotest (with and without metabolic activation) and the GreenScreen Assay using yeast S. cerevisiae. All tested compounds showed significant effects in most of the assays with lowest-observed-effect concentrations and concentrations causing 50% effects (EC50s) values ranging within microg/L to mg/L. The most toxic compound was 5-fluorouracil in the assays with P. putida (EC50 = 0.027 mg/L) and P. subcapitata (EC50 = 0.11 mg/L), although cisplatin and doxorubicin were the most toxic to D. magna (EC50 = 0.64 and 2.0 mg/L, respectively). These two chemicals were also the most genotoxic in the SOS-chromotest (minimum genotoxic concentrations [MGC] = 0.07-0.2 mg/L), and 5-fluorouracil was the most genotoxic in the eukaryotic yeast assay (MGC = 0.02 mg/L). Our investigation seems to indicate generally lower risks of acute effects at concentrations expected in the environment. However, some effective concentrations were relatively low and chronic toxicity of cytostatics (and/or their transformation products), as well as specific sources of human pharmaceuticals such as hospital effluents, require research attention.     

Potential for 4-n-nonylphenol biodegradation in stream sediments

The potential for in situ biodegradation of 4-nonylphenol (4-NP) was investigated in three hydrologically distinct streams impacted by wastewater treatment plants (WWTPs) in the United States. Microcosms were prepared with sediments from each site and amended with [U-ring-(14)C]4-n-nonylphenol (4-n-NP) as a model test substrate. Microcosms prepared with sediment collected upstream of the WWTP outfalls and incubated under oxic conditions showed rapid and complete mineralization of [U-ring-(14)C]4-n-NP to (14)CO(2) in all three systems. In contrast, no mineralization of [U-ring-(14)C]4-n-NP was observed in these sediments under anoxic (methanogenic) conditions. The initial linear rate of [U-ring-(14)C]4-n-NP mineralization in sediments from upstream and downstream of the respective WWTP outfalls was inversely correlated with the biochemical oxygen demand (BOD) of the streambed sediments. These results suggest that the net supply of dissolved oxygen to streambed sediments is a key determinant of the rate and extent of 4-NP biodegradation in stream systems. In the stream systems considered by the present study, dissolved oxygen concentrations in the overlying water column (8-10 mg/L) and in the bed sediment pore water (1-3 mg/L at a depth of 10 cm below the sediment-water interface) were consistent with active in situ 4-NP biodegradation. These results suggest WWTP procedures that maximize the delivery of dissolved oxygen while minimizing the release of BOD to stream receptors favor efficient biodegradation of 4-NP contaminants in wastewater-impacted stream environments.     

Physiological analysis of silver nanoparticles and AgNO3 toxicity to Spirodela polyrhiza

Silver nanoparticles (AgNPs) are commonly used in consumer products for their antibacterial activity. Silver nanoparticles may adversely influence organisms when released into the environment. The present study investigated the effect of AgNPs on the growth, morphology, and physiology of the aquatic plant duckweed (Spirodela polyrhiza). The toxicity of AgNPs and AgNO(3) was also compared. The results showed that silver content in plant tissue increased significantly with higher concentrations of AgNPs and AgNO(3) . Silver nanoparticles and AgNO(3) significantly decreased plant biomass, caused colonies of S. polyrhiza to disintegrate, and also resulted in root abscission. Physiological analysis showed that AgNPs and AgNO(3) significantly decreased plant tissue nitrate-nitrogen content, chlorophyll a (Chl a) content, chlorophyll a/b (Chl a/b), and chlorophyll fluorescence (Fv/Fm). Changes in soluble carbohydrate and proline content were also detected after both AgNO(3) and AgNPs treatment. However, after 192 h of recovery, total chlorophyll content increased, and Fv/Fm returned to control level. Median effective concentration (EC50) values for Chl a and phosphate content showed that AgNO(3) was more toxic than AgNPs (EC50 values: 16.10 ± 0.75 vs 7.96 ± 0.81 and 17.33 ± 4.47 vs 9.14 ± 2.89 mg?Ag?L(-1) , respectively), whereas dry-weight EC50 values showed that AgNPs were more toxic than AgNO(3) (13.39 ± 1.06 vs 17.67 ± 1.16 mg?Ag?L(-1) ).     

Laboratory degradation studies of four endocrine disruptors in two environmental media

We investigated the degradation of 17beta-estradiol (E(2)), 17alpha-ethinylestradiol (EE(2)), bisphenol-A (BPA), and 4-n-nonylphenol (4-n-NP) in river water-sediment and groundwater-aquifer material under aerobic and anaerobic conditions. The results showed rapid degradation of all four compounds in both media with >90% of the four compounds degraded within the first 2 to 4 d under both conditions. However, degradation rates were extremely slow for the remaining period. Model derived 50% dissipation time (DT50) values in river water-sediment slurries ranged from 0.24 to 1.5 d (E(2)), 0.29 to 1.1 d (EE(2)), 1.2 to 1.4 d (BPA), and 0.42 d (4-n-NP), while the 90% dissipation time (DT90) values for the four endocrine-disrupting chemicals (EDCs) ranged from 0.9 to 2.8 d under both conditions. A minor difference was observed in DT50 and DT90 values for the four EDCs in groundwater- aquifer material under aerobic conditions as compared with river water-sediment. Under anaerobic conditions, DT90 values ranged from >1,000 d (EE(2)) to >300 d (BPA), in groundwater-aquifer material. Degradation of the four compounds under anaerobic conditions was attributed to the sulfate-, nitrate-, and iron-reducing conditions within the tested media; however, it was postulated that overall degradation of the compounds was also influenced by abiotic factors, accounting for nearly 6 to 40% (river water- sediment) and 0 to 18% (groundwater-aquifer material) under the two conditions tested.