Effects of an herbicide and insecticide mixture in aquatic mesocosms

A 1.8 m×2.5 cm reciprocating-plate countercurrent extraction column was evaluated for the preparation of WSF (water-soluble fractions) from Flotta North Sea light crude oil. The energy input from the plate reciprocation speeds was found to be the main factor affecting the characteristics of the extracted WSF, and the throughputs of the stock solution or the ratio of seawater to crude oil had little effect on the concentration and composition of the extracted WSF. A combination of a reciprocation speed of 170 strokes/min, a seawater flow rate of 220 ml/min, and a crude oil flow rate of 2.9 ml/min produced a WSF stock solution with a total hydrocarbon concentration of 13.5±0.30 mg/kg (n=6) which was more reproducible than that made by a previously used large-scale batch extraction method. A settlement time of 5 h or less for the stock solution allowed a full separation of any dispersed droplets of crude oil from the aqueous phase under the above conditions, but further increases in reciprocation speeds caused difficulties in the final separation of this crude oil. The column extraction method was highly reproducible and gave a more concentrated WSF containing a higher proportion of alkanes than a WSF made by the batch extraction method. Low-boiling aromatics were the main components of the total extracted hydrocarbons of the WSF.     

Fate and effects of mercury in marine plankton communities in experimental enclosures

The development of a North Sea coastal plankton community exposed to different degrees of mercury stress in six simultaneously filled plastic bags was followed for 44 days. Mercuric chloride was added to four bags to yield concentrations of 0.5 (one bag), 5 (two bags), and 50 μg Hg · liter^?1 (one bag) in the water. Two bags served as controls. It could be shown that a single dose of 0.5 μg Hg · liter^?1 altered the species composition of the algal community on the walls of the bag. Addition of 5 μg Hg · liter^?1 had a marked impact on the development of the phytoplankton, as well as on that of the zooplankton and decomposers. Addition of 50 μg Hg · liter^?1 caused inactivation or death of the phytoplankton and zooplankton. The toxicity of mercuric chloride to the phytoplankton depends on (a) the concentration of the mercury, and (b) the particle concentration, i.e., the surface area available for adsorption of mercury. For this second reason the ratio between numbers of living cells and inanimate particles is an important factor influening mercury toxicity in aquatic ecosystems. Methylation of the added mercury occurs in the sediment of the bags after a lag phase of 1 month. Most of the added mercury disappears from the system by volatilization to metallic mercury. The remainder is absorbed by the sediment and the walls of the bags.     

Effect of herbicide residues on microbial processes in pond sediment

An assay system is described for examination of potential effects of herbicides on non-target sediment microorganisms. A key feature was to standardize a procedure for collecting and incubating intact miniature soil samples for assaying a variety of microbial activities. Potted pond sediment compared to undisturbed sediment cores showed no difference in initial carbon mineralization, acetylene reduction, phosphatase, and dehydrogenase activities, but did show a significant difference in methanogenesis. CuSO₄, after one week in pond sediment, inhibited phosphatase activity (1,000 ppm CuSO₄) and methanogenesis (20-1,000 ppm CuSO₄); no effect was noted for acetylene reduction, dehydrogenase activity and glucose mineralization. Simazine stimulated pond sediment acetylene reduction (1,000 ppm simazine); inhibited phosphatase activity (1,000 ppm simazine) and methanogenesis (50-1,000 ppm simazine); and had no effect on dehydrogenase activity and glucose mineralization. Chronic effects and effects at lower concentrations by these herbicides were less apparent. The results support the concept that a battery of tests are required to profile and evaluate the effects of herbicides on sediment microbial communities.     

Effects of road deicer (NaCl) and amphibian grazers on detritus processing in pond mesocosms

Road deicers have been identified as potential stressors in aquatic habitats throughout the United States, but we know little regarding associated impacts to ecosystem function. A critical component of ecosystem function that has not previously been evaluated with respect to freshwater salinization is the impact on organic matter breakdown. The purpose of this study was to evaluate cumulative effects of road deicers and tadpole grazers on leaf litter breakdown rate (g d(-1) ) and microbial respiration (mg O(2) g leaf(-1) h(-1) ). To test this interaction, in May 2008 the authors added dry leaf litter (Quercus spp.) to forty 600-L pond mesocosms and inoculated each with algae and zooplankton. In a full-factorial design, they manipulated a realistic level of road salt (ambient or elevated at 645?mg?L(-1) Cl(-) ) and tadpole (Hyla versicolor) presence or absence. The elevated chloride treatment reduced microbial respiration by 24% in the presence of tadpoles. The breakdown of leaf litter by tadpoles occurred 9.7% faster under ambient chloride conditions relative to the elevated chloride treatment. Results of the present study suggest that the microbial community is directly impacted by road deicers and heavy tadpole grazing under ambient conditions limits microbial capacity to process detritus. Road salts and tadpoles interact to limit microbial respiration, but to a lesser extent leaf mass loss rate, thereby potentially restricting energy flow from detrital sources in pond ecosystems. Environ. Toxicol. Chem. 2012; 31: 2306-2310. ? 2012 SETAC.     

Effects of the herbicide imazapyr on benthic macroinvertebrates in a logged pond cypress dome

Increased herbicide use in silviculture over the last several decades has led to concern over potential water contamination, which may affect biotic health. In the southeastern United States, pine flatwoods are important for timber production and are often interspersed with cypress wetlands. Cypress domes are isolated, shallow basins that collect surficial waters from adjacent forested areas and therefore might be expected to contain pesticide from storm runoff. This study utilizes in situ microcosm experiments to assess the effects of a concentration gradient of the herbicide imazapyr (0.184, 1.84, and 18.4 mg/L, equivalent to 1, 10, and 100 times the expected environmental concentration from a normal application rate) on the macroinvertebrate community of a logged pond cypress dome using changes in macroinvertebrate composition, chironomid biomass, and chironomid head-capsule deformities. The control core was not significantly different from the surrounding cypress dome for any parameter, suggesting that enclosure effects were likely of minimal importance in the final experimental results. The lack of statistical difference (p < 0.05) in macroinvertebrate community composition, chironomid deformity rate, and chironomid biomass between treatments suggests that imazapyr did not affect the macroinvertebrate community at the concentrations tested. Chironomid deformity rate ranged from 0.97% for imazapyr control to 4.96% for the 100x treatment, with chironomid biomass being 1.79 and 1.87 mg/L, respectively.     

Combined effects of a herbicide (atrazine) and predation on the life history of a pond snail, Physa gyrina

We investigated the combined effects of chronic pesticide exposure and predation on the life-history traits of Physa gyrina. Results show that atrazine and predation can impact snail immune function, reproduction, and survival. This work emphasizes the need to assess sublethal life-history responses to multiple stressors over biologically relevant timescales.     

Fate and effects of 4-chlorophenol and 2,4-dichlorophenol in marine plankton communities in experimental enclosures

The fate and effects of 4-chlorophenol (4CP) and 2,4-dichlorophenol (DCP) added to North Sea coastal plankton communities enclosed by large plastic bags were studied in three experiments of 4 to 6 weeks duration. The biodegradation of the compounds was studied in laboratory experiments using water from the enclosed ecosystems. 4CP and DCP, added at initial concentrations of 0.1-1.0 mg X liter-1, disappeared from the water in the enclosures in 5 to 23 days, 4CP generally being the less persistent. Degradation rates were generally comparable to those found in laboratory tests with the same water. 4CP was removed by biodegradation, and DCP was probably removed by a combination of biodegradation, photodegradation, and/or chemical degradation. Results indicated that biodegradation rates could be limited by lack of inorganic nutrients, leading to much lower degradation rates than would be expected from routine laboratory tests. Faster degradation after repeated addition of 4CP showed adaption of the bacterial community. Addition of 0.3 mg liter-1 4CP or DCP inhibited the phytoplankton growth rate slightly. The 1 mg liter-1 4CP or DCP inhibited the phytoplankton, changed the species composition, and also influenced the zooplankton. In two of the three experiments 1 mg liter-1 DCP resulted in a temporary lowering of bacterial numbers following the addition. In one experiment inhibitory effects were found after 4CP and DCP had disappeared from the water, pointing to the formation of a more toxic intermediate during the degradation of these compounds. The laboratory tests also indicated the formation of relatively stable intermediates. The concentrations causing the effects in the different bag experiments were quite similar. This indicates that, although the development of the plankton communities during the different experiments was different, the concentrations resulting in ecological effects are quite reproducible.     

Fate and effects of 3,4-dichloroaniline (DCA) in marine plankton communities in experimental enclosures

The fate and effects of single doses of 3,4-dichloroaniline (DCA) on North Sea coastal plankton communities enclosed by large plastic bags (contents 1.5 m3) were studied in two experiments lasting 5 and 6 weeks, respectively. The biodegradation of DCA was also studied in laboratory experiments, which were carried out simultaneously, using water from the enclosed model ecosystems. DCA was not degraded in the laboratory tests and probably also not degraded in the enclosed plankton communities, although concentrations in the water decreased during the experiments. This decrease appeared to be partly caused by diffusion of DCA through the walls of the enclosures. After the addition of single doses of 2, 10, and 25 microgram liter-1 DCA no effects on the enclosed plankton community could be detected. The addition of 0.1 mg liter-1 DCA had a clear influence on the species composition and the biomass development of the phytoplankton, changed the relative species composition of the zooplankton, and resulted in lower numbers of bacteria. In addition to these effects 1 mg liter-1 DCA limited the phytoplankton growth and resulted in mortality and inhibition of growth of the copepods.     

Fate and kinetics of carfentrazone-ethyl herbicide in California, USA, flooded rice fields

Little is known of the environmental fate of the aryltriazolinone herbicide carfentrazone-ethyl (compound I). Rice field applications of Shark 40D commercial formulation to duplicate 5.7 m2 rings (119 g a.i./ha) and 464 m2 commercial basins (224 g a.i./ha) produced pseudo-first-order half-lives (t1/2) of 6.5 to 11.1 h in water and 37.9 to 174 h in sediment. The rapid dissipation from water was due to its hydrolysis to the chloropropionic acid (compound II), which further degraded to its propionic, cinnamic, and benzoic acids. Compound I degraded similarly in soil, but propionic and cinnamic acid levels were higher. Compound I was only weakly adsorbed, but lateral movement of compound II through soil occurred. Laboratory hydrolysis produced quantitative yields of compound II, t1/2 values of 131 h at pH 7 and 3.36 h at pH 9, and slow dissipation at pH 5 (43% at 830 h). Ultraviolet (UV) irradiation of compound I in pH 7 buffer gave dissipation rates similar to those in dark controls (t1/2 113 h vs 128 h), while compound II was comparatively stable to photolysis (t1/2 765 h) and also did not volatilize from water. Ester hydrolysis followed by off-site movement of the acid (compound II) account for the dissipation of compound I.     

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.     

Laboratory and field responses to cadmium: an experimental study in effluent-dominated stream mesocosms

Although select stream flows in the southwestern United States are dominated by effluent discharges, metal hazards have not been experimentally evaluated in effluent-dominated streams. Lotic mesocosms were designed to assess cadmium effects on multiple levels of biological organization, to determine relevance to regulatory criteria of standard laboratory toxicity tests, and to link laboratory tests to stream responses. Replicate streams were treated with 15 or 143 microg/L Cd during a 10-d study. Streams were sampled on days 0 and 10 for benthic macroinvertebrates, periphyton, and ecosystem metabolism. Concurrent Ceriodaphnia dubia and Pimephales promelas laboratory tests were performed with water from streams. Individual organism, population, and community response variables were affected by 143 microg/L Cd but not by the I5-microg/L treatment level. A biotic ligand model for cadmium predicted a 48-h median effective concentration (EC50) value of 280 microg/L Cd for C. dubia in these effluent-dominated streams: an EC50 value of 38.3 microg/L Cd was estimated for C. dubia in tests performed with reconstituted hard water. Our findings generally support use of the biotic ligand model for establishing site-specific, acute water quality criteria for cadmium. However, future effluent-dominated stream research is required to evaluate relationships between chronic cadmium exposure and organismal and community responses.     

Fate of 2,4,6-trichlorophenol,pentachlorophenol,p-chlorobiphenyl,and hexachlorobenzene in an outdoor experimental pond: Comparison between observations and predictions based on laboratory data

2,4,6-Trichlorophenol, pentachlorophenol,p-chlorobiphenyl, and hexachlorobenzene were sprayed over an outdoor experimental pond and their time-dependent changes in concentration in sediment, fish, and water samples were determined for a period of 60 days. A model was assumed which described the movement and distribution of the compounds in the system. The rate constants for volatilization of these compounds from water, accumulation and excretion by fish, sediment sorption and desorption, and photolysis were also determined in laboratory experiments. The concentrations of these compounds were estimated, based on the hypothesis that the compound transfer could be expressed as a first-order rate process. It was demonstrated that the concentration changes of these compounds in the outdoor experimental pond could be estimated roughly from the model and the rate constants which had been determined in laboratory experiments.     

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.     

Influence of isolation on the recovery of pond mesocosms from the application of an insecticide. II. Benthic macroinvertebrate responses

The immediate response and recovery of the macrobenthic communities of nonisolated and isolated freshwater outdoor 9 ml mesocosms following an acute stress caused by the addition of deltamethrin were studied over a 14-month period. To discriminate between internal and external recovery mechanisms, half of the treated ponds were covered by 1-mm mesh lids that restricted aerial recolonization. Both structural (abundance of the different taxonomic groups) and functional (litter breakdown) parameters were monitored. Insects were broadly reduced in numbers by deltamethrin addition. In general, noninsect groups were not affected or increased in abundance in deltamethrin-treated ponds, probably because of relative insensitivity to deltamethrin, reduced predation, and lower competition for food. No major change in litter breakdown rates were seen, probably because of functional redundancy among the macrobenthic community. Chironominae larvae recovered in open, treated mesocosms 62 d after deltamethrin addition and most insect groups recovered 84 d after the treatment date. However, the presence of lids significantly reduced insect recovery rate, suggesting that it largely depends on the immigration of winged forms (i.e., external recovery) from surrounding non- or less affected systems. These results indicate that the recovery time of macrobenthic communities in an affected natural pond would depend on spatial characteristics of the landscape and also the season that exposure occurs. Isolated ecosystems would display posttreatment insect recovery dynamics very different from highly connected ones, evolving toward alternate pseudoequilibrium states, possibly with lower biodiversity but with preserved functionality. Consequences for higher tier risk assessment of pesticides are discussed.