Effects of diquat on freshwater microbial communities

A static microcosm system was used to evaluate effects of the herbicide diquat (0.3–30 mg/L) on the structure and function of naturally derived microbial communities on polyurethane foam substrates. Microbial communities were exposed to a single application of diquat and were monitored for 21 days. Effects on community structure included changes in algal cell density at diquat concentrations 0.3 mg/L (after an initial decrease in net productivity), bacterial cell density (1 mg/L diquat), and increased biomass accumulation (10 and 30 mg/L diquat). The species richness of protozoa was reduced at diquat concentrations >0.3 mg/L; protozoan species composition was progressively more dissimilar with diquat treatment. Effects on community function included inhibition of net productivity and community respiration (10 and 30 mg/L diquat), and decreased enzyme activities [alkaline phosphatase (1, 10, and 30 mg/L diquat), electron transport system (0.3 mg/L diquat), and -glucosidase (0.3 mg/L diquat)]. Both photosynthetic and nonphotosynthetic organisms were affected by diquat. Most structural and functional responses were sensitive indicators of stress. Estimated chronic toxicity values ranged from 0.3 mg/L (day 3) to 5.5 mg/L (day 21). Most microbial responses indicated that microbial community structure and function did not recover within the 21-day exposure period.     

Effects of short-term pulses of atrazine on attached algal communities in a small stream

The impact of short-term atrazine exposures on attached algal community composition and standing crop was investigated during the summer in a small, spring-fed stream in western Nebraska. Replicate trays of clay tiles were anchored to the stream bed, allowed to colonize for two weeks, then enclosedin situ with plexiglass boxes and exposed to a pulse of atrazine at 0, 2, 30, or 100 g/L for 24 hr. A second 24-hr atrazine pulse was applied two weeks later. Atrazine did not have a significant effect on cell densities of the dominant algae or the ash-free dry weight biomass of the periphyton community. The absence of observed treatment effects was likely due to the low but realstic levels of atrazine used and the transient nature of the application. Sediment deposition had a much greater influence on the attached algal community than short-term pulses of the herbicide.     

Effects of the antibiotic ciprofloxacin on stream microbial communities and detritivorous macroinvertebrates

Microbial communities play an important role in stream ecosystem processes, such as breakdown of senescent leaf litter, and as a primary nutritional source for detritivorous macroinvertebrates. Antibiotics may affect stream microbial communities and associated ecosystem processes, especially because recent stream and river monitoring programs have indicated the presence of antibiotics downstream of wastewater treatment plants. In the current study, effects of chronic exposure to the fluoroquinolone antibiotic ciprofloxacin (Cipro) were examined on stream microbial community-level physiological profiles and growth indices of detritivorous amphipods (Gammarus spp.) and caddisflies (Lepidostoma liba). Microcosm experiments were conducted using stream sediments and water, senesced leaf material (Acer saccharum), and macroinvertebrates. A shift in function of leaf-associated microbial communities (based on carbon source utilization) was observed for samples exposed to 100 microg/L of Cipro for 12 d compared to control and treatments exposed to 1 and 10 microg/L of Cipro. This was attributable to carbohydrate substrates, which had 2.7- to 3.5-fold lower microbial respiration than the lower concentrations and control (p < 0.001). For detritivores, Gammarus spp. condition index did not differ among control, 0.1, and 1.0 microg/L treatments after 30-d exposures (p > 0.05). Similarly, L. liba growth rate did not vary among control, 10, and 100 microg/L treatments after 45-d exposures (p > 0.05). These results suggest that Cipro may affect leaf-associated microbial communities, but at concentrations four orders of magnitude above those detected in streams. However, effects of the antibiotic on growth and condition of detritivores were not observed. Future work should focus on identifying specific changes in stream microbial communities as a result of Cipro exposure and impacts on other aquatic species.     

Effects of linear alkylbenzene sulfonates on functional diversity of microbial communities in soil

Linear alkylbenzene sulfonates (LAS) often occur in sewage sludge that is applied to agricultural soil. Here LAS may affect the microbial activity, which is an important basis for nutrient cycling. Previous studies have shown that single bacterial species and specific soil processes can be very sensitive to LAS. Here we report that two levels of LAS, 22 and 174 mg/kg dry weight soil, had little or no significant influence of the functional diversity of bacteria in a sandy soil, as tested by community-level physiological profiles. Briefly, these profiles are a characterization of the microbial communities based on the pattern of substrate utilization in 96-well microtiter plates (Biolog EcoPlates). Sandy agricultural soil was incubated in duplicate 1-L mesocosms with or without LAS, and bacteria were extracted after one, two, and four weeks. During incubation, more than 98 and 93% of LAS added to 22 and 174 mg/kg dry weight soil was degraded, respectively. The presence of LAS at 174 mg/kg dry weight caused a higher number of bacteria in the soil extracts, maximally corresponding to 2.5 times the numbers in LAS-free soil (1.8 x 10(7) cells/g dry wt soil) after four weeks of incubation. No inhibitory effect of LAS was observed when the substrate utilization data were analyzed for substrate richness and diversity (Shannon-Weaver indices). Principal component analysis, however, showed that the pattern of substrate utilization in soil with the highest LAS content (174 mg/kg dry wt) could be distinguished from control soil and soil with 22 mg LAS/kg dry weight. Yet the overall conclusion was that the functional diversity of the aerobic, heterotrophic bacterial community was rather insensitive to LAS.     

Effects of large-scale poultry farms on aquatic microbial communities: a molecular investigation

The effects of large-scale poultry production operations on water quality and human health are largely unknown. Poultry litter is frequently applied as fertilizer to agricultural lands adjacent to large poultry farms. Run-off from the land introduces a variety of stressors into the surface waters including nutrients, antimicrobials and pathogenic bacteria. The Delaware, Maryland and Virginia (Delmarva) Peninsula has the highest concentration of broiler chickens per farm acre in the United States and provides an ideal location for studying the effects of stressors from poultry farms. We investigated potential effects by characterizing shifts in the structure of aquatic bacterial communities. DNA was isolated from microorganisms in water samples from streams and rivers at varying distances from, or having different frequencies of, litter applications. Fingerprints of 16S rDNA amplicons from bacteria in water samples collected during late summer 2001 to late spring 2002 were produced by denaturing gradient gel electrophoresis (DGGE). A statistical analysis of multiple fingerprints from each sampling location demonstrated that each site harboured a bacterial community significantly different from the communities at other sites. Similarly, the bacterial communities from each sampling time differed significantly from communities at other sampling times. Most importantly, a competitive, library-based analysis showed time of sampling (month) had a greater effect on community structure than did location.     

Effects of time-variable exposure regimes of the insecticide chlorpyrifos on freshwater invertebrate communities in microcosms

The present study compared the effects of different time-variable exposure regimes having the same time-weighted average (TWA) concentration of the organophosphate insecticide chlorpyrifos on freshwater invertebrate communities to enable extrapolation of effects across exposure regimes. The experiment was performed in outdoor microcosms by introducing three different regimes: a single application of 0.9?μg active ingredients (a.i.)/L; three applications of 0.3?μg a.i./L, with a time interval of 7?d; and continuous exposure to 0.1?μg a.i./L for 21?d. Measurements showed that the TWA(21d) concentration in the continuous-exposure treatment (0.098?μg/L) was slightly lower than in the three-application (0.116?μg/L) and single-application (0.126?μg/L) treatments. The application of chlorpyrifos resulted in decreased abundances in the arthropod community, with the largest adverse effects reported for the mayfly Cloeon dipterum and cladocerans Daphnia gr. longispina and Alona sp., while smaller effects were observed for other insects, copepods, and amphipods. At the population level, however, the mayfly C. dipterum only responded to the single-application treatment, which could be explained by the toxicokinetics of chlorpyrifos in this species. At the end of the experimental period the invertebrate community showed approximately the same effect magnitude for all treatment regimes. These results suggest that for this combination of concentrations and duration of the TWA, the TWA concentration is more important for most species than the peak concentration for the assessment of long-term risks of chlorpyrifos.     

The effects of atrazine on microcosms developed from four natural plankton communities

Comparisons were made among Leffler microcosms developed from four different natural communities and exposed to 0, 20, 100, 200, 500, 1,000, and 5,000 g/L atrazine, a commonly used herbicide. Atrazine reduced net primary productivity, pH, and net productivity/respiration ratios in all four microcosm communities. In three of the four communities, the lowest observed (P < 0.05) effect concentration (LOEL) was 100 g/L. In the fourth community the LOEL was 200 g/L atrazine.The sensitivity and accuracy of bioassays with four different microcosm communities were evaluated by comparing results with values reported for acute and chronic single species bioassays, other types of microcosms, and experimental ponds exposed to similar concentrations of atrazine. The ranges of sensitivity noted in these experiments were less than the range reported for single species bioassays using common test organisms and similar to those reported for other microcosms. The similarity between Leffler microcosm results and the responses reported for the experimental ponds suggests that the Leffler microcosms accurately reflected concentrations causing ecosystem level changes in the experimental ponds.     

Studies on the degradation of atrazine by bacterial communities enriched from various biotopes

Degradation of¹⁴C-ring labeled atrazine (2-choloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) by bacterial populations from soil, waters and activated sludges was investigated and compared with non-biological decomposition in sterile solutions. Within two weeks, 0.6% Cl-deethyl- and 0.1% Cl-deisopropylatrazine had been formed in sterile 0.02 M phosphate buffer, pH 7.2. In biodegradation studies, bacterial populations were enriched and incubated in media containing atrazine and high or low levels of nutrients. Nutrient supply had a strong effect on the fate of atrazine in bacterial cultures, whereas the origin of bacteria was of minor importance. In 31 of 33 mixed populations investigated, the herbicide was largely converted to unidentified compounds. Incubation with high levels of nutrients resulted in 17% to 57% of these compounds being constant after one and two weeks of incubation. In parallel experiments with low nutrient supply, the compounds were present in amounts of 7% to 57% after one week. The proportions of the unidentified compounds dropped within the second week of incubation, while atrazine reappeared correspondingly. The amounts of dealkylated metabolites generally did not exceed those of sterile solutions. The results indicate that atrazine is not degraded by bacteria but bound, thus simulating biodegradation. Evidence is presented that physicochemical decomposition of the herbicide is more significant than microbial degradation.     

Effects of atrazine and paraquat on nitrifying bacteria

The influence of atrazine and paraquat on a mixed culture of nitrifying bacteria was studied in an aqueous system. At a concentration as low as 1 g/mL paraquat exerted a complete inhibition of ammonium and nitrite oxidation for 40 days. Atrazine (1 g/mL and 2 g/mL), however, caused only an inhibition of ammonium oxidation for a short period. After 16–18 days of inhibition the ammonium oxidizing activity was resumed. In the presence of atrazine (1 g/mL), however, the rate of nitrite oxidation was increased. Within a period of 28 days, in culture media a partial degradation of atrazine occurred.     

Environmental levels of atrazine decrease spatial aggregation in the freshwater mussel,Elliptio complanata

The commonly used herbicide atrazine (ATR), may cause estrogen-like alterations and, like other xenoestrogens, may alter behavior. Here effects on animal aggregation were tested in freshwater mussels exposed short-term to ecologically relevant ATR concentrations between 1.5 and 150 μg/L. The aggregation index (AI), the fraction of mussels in the most densely populated tank section, was evaluated and showed higher AI at later times in both 6- and 72-h trials (p<0.001). After 72 h, there was also less aggregation in estradiol- and mid-ATR-treated animals, 26% and 24% less than control, respectively (p<0.04). These data suggest that freshwater mussels tend to aggregate, that 72-h exposure to ecologically relevant ATR concentrations decreases aggregation, and that estradiol exposure has a similar effect. Given that bivalve aggregation may be related to reproduction, the results suggest that low concentrations of ATR may have ecological consequences on animal populations in this species.     

Influence of 4-nonylphenol on the structure of nematode communities in freshwater microcosms

We investigated the effect of 4-nonylphenol (NP) on nematode communities in the sediment of freshwater microcosms. Seven treatments were dosed with various concentrations of NP over a period of six weeks by using a controlled-release method (NPI-NP7; maximum sediment concentrations: 0.29-3.37 mg/kg dry wt). Four microcosms were not exposed to NP and served as controls. Nematode communities were analyzed over a period of 15 weeks, including sampling dates before, within, and after the NP application. Communities were characterized in terms of total nematode abundance and species diversity (Shannon index and evenness), as well as composition of species, feeding types, and different life-history strategists (maturity index [MI]). Species composition was analyzed by using a multivariate method (principal response curves). Total nematode abundance and species diversity were not affected in any of the NP-treated microcosms. However, in the highest dosed treatment, NP-induced changes in the nematode communities occurred. Species and feeding types composition, as well as the MI, were affected in the postapplication period, with species composition being altered most clearly. In the highest dosed treatment, deposit-feeding species, classified as colonizers (Eumonhystera), increased in dominance, whereas epistrate feeders and chewers (Prodesmodora and Tobrilus) decreased in relative abundance compared to the control.     

Response of zooplankton communities to liquid creosote in freshwater microcosms

In this study, the response of zooplankton communities to single applications of liquid creosote in model aquatic ecosystems (microcosms) was evaluated. Liquid creosote was applied to 14 microcosms at concentrations ranging from 0.06 to 109 mg/L. Two microcosms served as controls. Zooplankton samples were collected from each microcosm on days 7 and 1 before treatment and on days 2, 5, 7, 14, 21, 28, 43, 55, and 83 following treatment. Temporal changes (response-recovery) in composition of the zooplankton community were assessed using principal response curves (PRC). Creosote induced a rapid, concentration-dependent reduction in zooplankton abundance and number of taxa, with maximum response (50-100% reduction in population densities) occurring between 5 and 7 d after treatment. Taxa that dominated at the time of treatment experienced the greatest impact, as indicated by large, positive species weight values (> 1) from the PRC analysis. Many of these taxa recovered to pretreatment or control levels during the posttreatment period, with the degree and duration of recovery being strongly dependent on concentration. Creosote had little effect on species composition at less than 1.1 mg/L, because changes in the types and relative proportion of species contributed from Cladocera, Rotifera, and Copepoda were comparable to those observed in control microcosms. However, a significant shift in species composition was observed at concentrations greater than 1.1 mg/L; these microcosms were generally dominated by low numbers of rotifers, some of which had not been collected before treatment. Community-level effect concentrations (EC50s) were 44.6 and 46.6 micrograms/L at 5 and 7 d, respectively, based on nominal creosote. Corresponding no-effect concentrations were 13.9 and 5.6 micrograms/L. The results of this field study indicate that creosote may pose a significant risk to zooplankton communities at environmental concentrations potentially encountered during spills and/or leaching events.     

Effects of fomesafen, alone and in combination with an adjuvant, on plankton communities in freshwater outdoor pond mesocosms

Ecotoxicological effects of the diphenyl ether herbicide fomesafen, applied alone or in combination with the adjuvant Agral 90 (mixture of polyethoxylated derivatives of nonylphenol), were assessed on planktonic communities in 18-m3 outdoor mesocosms during a nine-month study. Four mesocosms were treated with fomesafen only (nominal concentration: 40 microg/L), four were treated with the mixture fomesafen-Agral 90 (nominal concentration: 40 microg/L and 90 microg/L, respectively), and four were kept as the controls. Five treatments were performed every three weeks from April 18, 2000. Mean (+/- standard error [SE]) values of fomesafen concentration in water of 62.5 (+/-5.3) and 19.4 (+/-7.6) microg/L were measured at the end of the treatment period in fomesafen- and mixture-treated mesocosms, respectively. Fomesafen, either alone or in mixture with Agral 90, had a significant positive effect on the abundance and biovolume of Cyanobacteria, Cryptophyceae, Dinophyceae, and Bacillariophyceae. Chlorophyceae were inhibited by the herbicide and laboratory toxicity tests confirmed that green algae were more sensitive toward fomesafen than other algal classes. A positive effect of treatments on phytoplankton taxonomic diversity also was observed, indicating that, like natural disturbances of intermediate strength, xenobiotics sometimes may enhance the diversity of algal communities. Fomesafen alone did not have any clear effect on zooplankton. Abundance of calanoid copepods was reduced significantly in the mixture-treated ponds, suggesting either a direct effect of the adjuvant and/or an enhancement of herbicide toxicity by Agral 90. The abundance of other zooplanktonic herbivorous groups increased due to a reduced competition for food for herbivorous species and a higher availability of preys for predators. No algal bloom was observed in the treated ponds, presumably because of grazing pressure and the low availability of nutrients.     

Effects of the pesticides captan, deltamethrin, isoproturon, and pirimicarb on the microbial community of a freshwater sediment

In three microcosm experiments, we exposed microbial communities of a natural sediment to environmentally relevant concentrations of the fungicide captan, the herbicide isoproturon, and the insecticides deltamethrin and pirimicarb. Exposure concentrations were estimated negligible concentrations (NCs), maximum permissible concentrations (MPCs), and 100 times MPC (100MPC). Experimental endpoints were microbial community respiration and biomass, bacterial activity, and denitrification. All four pesticides inhibited bacterial activity by 20 to 24% at MPC, which corresponded to concentrations in the range of microg/kg dry-weight sediment. Treatments with deltamethrin and isoproturon showed inhibiting effects on bacterial activity at NC exposures. Surprisingly, for captan, deltamethrin, and isoproturon, this inhibiting effect was not observed at 100MPC treatments. Microbial biomass was negatively effected in MPC treatments with deltamethrin and in NC treatments with isoproturon. The tested pesticides did not affect community respiration and denitrification rates. These results show that exposure to the tested pesticides may induce toxic responses in sediment microbial communities at concentrations that are predicted to be environmentally safe.     

阿特拉津对小鼠腹腔巨噬细胞功能影响的体外研究

目的探讨阿特拉津(ATZ)体外染毒对小鼠腹腔巨噬细胞功能的影响,为其免疫毒性评价积累资料。方法分离培养小鼠腹腔巨噬细胞,经不同浓度(0~1000μmol/L)阿特拉津处理后,MTT比色法测定细胞活力,中性红(NR)法测定其吞噬功能,硝酸还原酶法测定NO含量,ELISA法测定TNF-α释放能力,DCFH-DA荧光标记流式细胞术测定活性氧含量。结果 MTT法测得ATZ对小鼠腹腔巨噬细胞的24、48、72 h染毒的IC50分别为(887.4±1.11)、(360.2±1.13)、(270.6±1.20)μmol/L。NR吸收法所测得各时间点IC50分别为(214.2±1.14)、(120.0±1.10)、(42.60±1.12)μmol/L。24 h及72 h染毒后,低浓度ATZ剂量组NO含量较对照组增加,高浓度剂量组NO含量较对照组出现下降趋势。72 h染毒后,低浓度ATZ剂量组(0.01、0.1μmol/L)TNF-α的含量高于对照组(P<0.05),但在1μmol/L及以上的ATZ染毒组TNF-α含量较对照组降低(P<0.05)。小鼠腹腔巨噬细胞在ATZ低剂量组(0.01、1μmol/L)染毒24 h和72 h时均能促使ROS的产生(P<0.05),但在100μmol/L剂量组里ROS释放量却降低。结论阿特拉津染毒可影响小鼠腹腔巨噬细胞的活性和吞噬功能,并可干扰其细胞因子/活性氧/活性氮的释放。