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.     

Petroleum hydrocarbon concentrations in a salmonid stream contaminated by oil field discharge water and effects on macrobenthos

The concentration of total hydrocarbons in the water effluent from an oil field was 5.6 mg/L and resulted in concentrations of 46 to 85μg/L in the receiving stream. Total hydrocarbons were 55,000 times more concentrated in the sediment than in the water, ranging from 979 (778) to 2,515 (1,263) mg/kg. Saturated hydrocarbons contributed most to the total hydrocarbon concentration in both water and sediment. Naphthalenes were found in stream water, but not in sediment. Cadmium, chromium, copper, lead, and zinc were detected in water and sediment. Zinc was elevated in the sediment, probably because an organic zinc complex was used by the oil company during processing to enhance oil-water separation. Species diversity of macrobenthos was reduced below the discharge, as evidenced by the almost complete elimination of Plecoptera and Trichoptera. Shannon-Weaver diversity index values ranged from 3.4 at the upstream control station to 1.2 to 1.7 below the oil field effluent. The representation of Diptera increased from 10% of the total insects at the least polluted station to 46% at the station containing the most dissolved hydrocarbons. On the basis of our findings, discharge of oil into fresh water should be closely regulated to prevent the development of concentrations in water and sediment of the receiving stream that would alter the structure of macrobenthos communities and thereby threaten the fishery resources.     

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.     

The effects of diflubenzuron on a complex laboratory stream community

Effects were assessed on the total biological community in complex laboratory streams caused by continuous exposure to diflubenzuron (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl) urea). The insect fauna suffered direct toxic effects at concentrations of 1.0g/L and greater. The algal and fungal floras were mildly affected at the same concentrations; apparently indirect effects in response to the reduced herbivore and shredder components of the insect fauna. No effects were observed on the bacteria, oligochaetes or gastropods, at any of the test concentrations. Within the insect fauna, differences in sensitivities were observed: mayflies and stoneflies were affected at 1.0g/L, dipterans were affected at 10.0g/L, and coleopterans were apparently unaffected at any of the test concentrations. Effects on caddisflies could not be determined due to their failure to become established in the stream systems. These differences between insect orders in sensitivity, coupled with differences in generation time, may reduce the overall benefits of the insecticide. For example, if diflubenzuron is used for chironomid control, the result may be more severe and longer lasting effects on nontarget mayfly and stonefly populations.     

Response of Zooplankton and Phytoplankton Communities to Creosote-Impregnated Douglas Fir Pilings in Freshwater Microcosms

Creosote has been used extensively as an industrial wood preservative for the protection of marine pilings, railway ties, and utility poles and is a common source of polycyclic aromatic hydrocarbons (PAHs) into aquatic environments. At present, there is little information by which to judge the potential for creosote leached from impregnated pilings to cause toxicity to biota in aquatic environments. The objective of the current study was to assess the effects of creosote on zooplankton and phytoplankton populations in freshwater microcosms in relation to changes in the concentration and composition of PAHs leached from creosote-impregnated Douglas fir pilings during an 83-day exposure period. The study consisted of single microcosms containing one half, one, two, three, four, and six treated pilings. Two microcosms that received untreated pilings were used as controls. The total surface area of pilings in each microcosm was normalized by adding the appropriate number of untreated pilings. Samples were collected periodically between –14 and 83 days pre- and post-exposure to determine aqueous concentrations of 15 priority PAHs and to assess the response of zooplankton and phytoplankton communities. Plankton community response to creosote was analyzed using principle responses curves. Peak aqueous concentrations of PAH occurred at day 7, ranging from 7.3 to 97.3 g/L. Zooplankton abundance decreased in all microcosms after introduction of the impregnated pilings, with the magnitude of response varying as a function of aqueous creosote concentration. Using inverse regression, a no-observed-effect concentration for the zooplankton community of 11.1 g/L was estimated. In contrast, algal abundance and diversity increased in all treatments between 7 and 21 days and attained levels up to twice that in control microcosms. This trend most likely reflected decreased grazing pressure because of the decrease in zooplankton populations, but it may also have reflected growth stimulation resulting from exposure to various constituents within the creosote mixture. Our results indicate that creosote leached from impregnated pilings deployed under typical conditions (e.g., wharves) may cause transient toxicity to benthic or limnetic communities shortly after deployment, but this likely poses few long-term risks to aquatic freshwater plankton communities.     

Environmental safety to decomposer invertebrates of azadirachtin (neem) as a systemic insecticide in trees to control emerald ash borer

The non-target effects of an azadirachtin-based systemic insecticide used for control of wood-boring insect pests in trees were assessed on litter-dwelling earthworms, leaf-shredding aquatic insects, and microbial communities in terrestrial and aquatic microcosms. The insecticide was injected into the trunks of ash trees at a rate of 0.2 g azadirachtin cm⁻¹ tree diameter in early summer. At the time of senescence, foliar concentrations in most (65%) leaves where at or below detection (<0.01 mg kg⁻¹ total azadirachtin) and the average concentration among leaves overall at senescence was 0.19 mg kg⁻¹. Leaves from the azadirachtin-treated trees at senescence were added to microcosms and responses by test organisms were compared to those in microcosms containing leaves from non-treated ash trees (controls). No significant reductions were detected among earthworm survival, leaf consumption rates, growth rates, or cocoon production, aquatic insect survival and leaf consumption rates, and among terrestrial and aquatic microbial decomposition of leaf material in comparison to controls. In a further set of microcosm tests containing leaves from intentional high-dose trees, the only significant, adverse effect detected was a reduction in microbial decomposition of leaf material, and only at the highest test concentration (∼6 mg kg⁻¹). Results indicated no significant adverse effects on litter-dwelling earthworms or leaf-shredding aquatic insects at concentrations up to at least 30× the expected field concentrations at operational rates, and at 6× expected field concentrations for adverse effects on microbial decomposition. We conclude that when azadirachtin is used as a systemic insecticide in trees for control of insect pests such as the invasive wood-boring beetle, emerald ash borer, resultant foliar concentrations in senescent leaf material are likely to pose little risk of harm to decomposer invertebrates.     

Ionic imbalance as a source of toxicity in an estuarine effluent

A toxicity identification evaluation (TIE) was conducted on the effluent from a petrochemical plant which discharges into an estuary. The effluent had been consistently toxic to mysid shrimp (Mysidopsis bahia) but not toxic to sheepshead minnows (Cyprinodon variegatus). Phase I effluent toxicity characterization tests revealed that treatment of the effluent with a cation exchange resin (Amberlite^® IR-120 Plus) was partially effective at reducing, but not removing, toxicity. Phase II characterization tests revealed that four cations varied with toxicity: Ca and Sn were positively correlated with increasing toxicity; Mg and K were negatively correlated with increasing toxicity. Toxicity tests with SnCl₂ revealed that the toxicity threshold for Sn was far above the concentrations present in the raw effluent. Reduction of Ca was shown to result in a significant improvement in survival, but some toxicity still remained. Further augmentation of the treated effluent with CaCl₂, MgCl₂, and KBr to restore the concentrations of Ca, Mg, K, and Br to natural seawater concentrations resulted in survival of all exposed organisms. Repeated success of this treatment regime on additional samples of the effluent as well as mock effluent studies confirmed that ion imbalance was the sole source of toxicity in this effluent. Process source water composition and essential ion balance are discussed as important components of marine effluent TIEs.     

Effluent-dominated streams. Part 2: Presence and possible effects of pharmaceuticals and personal care products in Wascana Creek, Saskatchewan, Canada

Recent worldwide surveys have not only established incomplete removal of pharmaceuticals and personal care products (PPCPs) by sewage treatment plants, but also their presence in surface waters receiving treated sewage effluent. Those aquatic systems where sewage effluent dominates flow are thought to be at the highest risk for ecosystem level changes. The city of Regina, Saskatchewan, Canada (population 190,400) treats its sewage at a modern tertiary sewage treatment facility located on Wascana Creek. The Wascana Creek hydrograph is dominated by one major event: spring snow melt. Thereafter, creek flow declines considerably and in winter treated sewage effluent makes up almost 100% of stream flow. Four water surveys conducted on the creek from winter 2005 to spring 2007 indicated that PPCPs were always present, in nanogram and sometimes microgram per liter concentrations downstream of the sewage treatment plant. This mixture included antibiotics, analgesics, antiinflammatories, a lipid regulator, metabolites of caffeine, cocaine and nicotine, and an insect repellent. Not surprisingly, concentrations of some PPCPs were highest in winter. According to hazard quotient calculations and homologue presence, ibuprofen, naproxen, gemfibrozil, triclosan, erythromycin, trimethoprim, and sulfamethoxazole were present in Wascana Creek at concentrations that may present a risk to aquatic organisms. The continual exposure to a mixture of pharmaceuticals as well as concentrations of un-ionized ammonia that far exceed Canadian and American water quality guidelines suggests that Wascana Creek should be considered an ecosystem at risk. Although the Wascana Creek study is regional in nature, the results highlight the considerable risks posed to aquatic organisms in such effluent-dominated ecosystems.     

Assessment of reproductive effects in largemouth bass (Micropterus salmoides) exposed to bleached/unbleached kraft mill effluents

This study evaluated the potential effects of different concentrations of bleached/unbleached kraft mill effluent (B/UKME) on several reproductive endpoints in adult largemouth bass (Micropterus salmoides). The kraft mill studied produces a 50/50 mix of bleached/unbleached market pulp with an estimated release of 36 million gal of effluent/day. Bleaching sequences were C₉₀d₁₀EopHDp and CEHD for softwood (pines) and hardwoods (mainly tupelo, gums, magnolia, and water oaks), respectively. Bass were exposed to different effluent concentrations (0 [controls, exposed to well water], 10, 20, 40, or 80%) for either 28 or 56 days. At the end of each exposure period, fish were euthanized, gonads collected for histological evaluation and determination of gonadosomatic index (GSI), and plasma was analyzed for 17β-estradiol, 11-ketotestosterone, and vitellogenin (VTG). Largemouth bass exposed to B/UKME responded with changes at the biochemical level (decline in sex steroids in both sexes and VTG in females) that were usually translated into tissue/organ-level responses (declines in GSI in both sexes and in ovarian development in females). Although most of these responses occurred after exposing fish to 40% B/UKME concentrations or greater, some were observed after exposures to 20% B/UKME. These threshold concentrations fall within the 60% average yearly concentration of effluent that exists in the stream near the point of discharge (Rice Creek), but are above the <10% effluent concentration present in the St. Johns River. The chemical(s) responsible for such changes as well as their mode(s) of action remain unknown at this time. Received: 3 January 2001/Accepted: 4 June 2001     

Macroinvertebrate responses along the recovery gradient of a regulated river (Spain) receiving an industrial effluent

Macroinvertebrate responses were examined along the recovery gradient of the regulated Río Duratón (northern Spain) receiving an industrial effluent. Hypolimnial releases from Burgomillodo Dam caused short-term flow fluctuations and low concentrations of dissolved oxygen at S-2, S-3, S-4, and S-5 sampling sites (0.2, 0.4, 2.5, and 7.6 km below the dam, respectively) compared with the upstream reference station (S-1). The industrial effluent caused a significant (P<0.05) increase in the fluoride concentration at S-3, S-4, and S-5 stations. Moreover, because of the differential discharge of hypolimnial waters from the dam, fluoride concentrations experienced a temporal variation over a one-day period at S-3, S-4, and S-5. The suspended inorganic matter (SIM) only increased significantly (P<0.05) just below the effluent (S-3), settling on the stream bottom of this sampling site. Tricladida, Amphipoda, Plecoptera and Coleoptera were the major macroinvertebrate groups most adversely affected. Total density (N), total biomass (B) and family diversity (D) were higher at S-1 than at downstream sampling sites, their values being lowest at S-3. The family uniformity (U) had its highest value at S-3. The family dominance (d) exhibited lower values at S-2, S-3, and S-4 than at S-1 and S-5. Shredders and collector-gatherers were the functional feeding groups most adversely affected, predators and filter-feeders increasing their abundances downstream from the dam. According to the River Continuum Concept, these changes in functional feeding groups reflect a potamonization (enhancement of potamic conditions) in the trophic structure of the macrobenthic community. The highest values of environmental impact (EI) were estimated at S-3 and the lowest values at S-5. The lowest value of percentage similarity (PS) was estimated between S-1 and S-3 and the highest value between S-4 and S-5. It is concluded that the major abiotic factors responsible for macroinvertebrate responses were short-term flow fluctuations and dissolved O₂ deficit at S-2, S-4, and S-5 sampling sites, and the siltation of SIM just below the industrial effluent (S-3). The fluoride pollution was a minor factor. In this sense, reductions in hypolimnial release and improvements in waste treatment are recommended in order to mitigate the adverse effects of the industrial effluent and Burgomillodo Dam on the structure of the macrobenthic community.     

Effects of Lindane on the Planktonic Community in Freshwater Microcosms

Effects of lindane on natural planktonic communities were investigated in aquatic indoor microcosms. Lindane was dosed to eight 300-liter microcosms for 2 weeks, and effects and recovery processes were monitored over 12 weeks. Mean measured water concentrations of lindane during the exposure period were 3, 6, 13, 27, 55, 102, 230, and 455 μg/liter. Zooplankton was severely affected by lindane. The most sensitive organisms were nauplii of copepodes which were affected at all treatment levels ≥6 μg/liter during exposure (Days 2–14). Recovery of nauplii abundance was concentration-dependent at concentrations ≤55 μg/liter lindane, whereas at concentrations ≥102 μg/liter recovery was negligible.Cladoceraabundance decreased during exposure to ≥102 μg/liter lindane and did not recover to original levels until the end of the study. For phytoplankton, decreased population densities ofChlorophyceaeand microalgae (<5 μm) were observed at lindane concentrations ≤55 μg/liter, where zooplankton was only temporarily affected. At higher lindane concentrations (≥102 μg/liter) effects on phytoplankton were not clear, as also increases in abundances were observed, probably as a consequence of minimized grazing pressure, due to high zooplankton mortality. Comparison of these results with data obtained in complex outdoor systems demonstrates the practicability and sensitivity of indoor microcosms and emphasizes the importance of long-term testing and assessment of recovery processes for prediction of environmental effects.     

Non-target effects on aquatic decomposer organisms of imidacloprid as a systemic insecticide to control emerald ash borer in riparian trees

Imidacloprid is effective against emerald ash borer when applied as a systemic insecticide. Following stem or soil injections to trees in riparian areas, imidacloprid residues could be indirectly introduced to aquatic systems via leaf fall or leaching. Either route of exposure may affect non-target, aquatic decomposer organisms. Leaves from ash trees treated with imidacloprid at two field rates and an intentionally-high concentration were added to aquatic microcosms. Leaves from trees treated at the two field rates contained imidacloprid concentrations of 0.8-1.3 ppm, and did not significantly affect leaf-shredding insect survival, microbial respiration or microbial decomposition rates. Insect feeding rates were significantly inhibited at foliar concentrations of 1.3 ppm but not at 0.8 ppm. Leaves from intentionally high-dose trees contained concentrations of about 80 ppm, and resulted in 89-91% mortality of leaf-shredding insects, but no adverse effects on microbial respiration and decomposition rates. Imidacloprid applied directly to aquatic microcosms to simulate leaching from soils was at least 10 times more toxic to aquatic insects than the foliar concentrations, with high mortality at 0.13 ppm and significant feeding inhibition at 0.012 ppm.     

Macroinvertebrate and periphyton response to streambed agitation for release of substrate-trapped hydrocarbons

Following a spill of more than 94.4 m³ of unleaded gasoline into Wolf Lodge Creek in northern Idaho, impacted areas were mechanically agitated to release substrate-trapped hydrocarbons by dragging a bulldozer blade with a tightly wound chainlink fence attached to it backward over the substrate. Portions of two riffles were left unagitated to determine if differential recovery of benthic macroinvertebrates and periphyton in cleaned vs uncleaned areas of the stream would occur. Chlorophyll a concentrations and densities of most macroinvertebrates were significantly lower (P 0.05) in raked areas 12 days after stream cleaning. However, macroinvertebrate and periphyton community compositions were very similar 1 month after stream cleaning and for the remainder of the study. In spite of similar recovery times of macroinvertebrates and periphyton in raked and nonraked areas, the cleaning process is viewed as beneficial because it minimized possible chronic effects on the biota without causing substantial additional impact.     

Changes in the aqueous behavior of parathion under varying conditions of pH

Factors affecting the stability of parathion in the aquatic environment were studied, with emphasis on pH. In 24-hr toxicity tests, using the midgeChironomus riparius, parathion was significantly more toxic at pH 6 than at pHs 4 and 8. While the data from toxicity tests suggested that pH may be important in determining the environmental fate of parathion, pH was found to be insignificant in controlling levels of parathion in water and organisms of aquatic microcosms adjusted to pHs 4, 6, and 8. After 7 days, parathion accounted for 29.7, 28.7, and 36.6% of total radioactivity in the water of microcosms held at pHs 4, 6, and 8, respectively. In abiotic water, however, no parathion breakdown was observed in 40 days at any of the three pH levels. These data demonstrate the importance of biotic factors, particularly microorganisms, in degrading parathion. Microorganisms which metabolize parathion in the microcosms were not adversely affected by changes in pH.     

The effects of microcosm size and substrate type on aquatic microcosm behavior and arsenic transport

The chemical and biological characteristics of 12 freshwater microcosms of two different sizes (7-L and 70-L) and substrate types (sand and lake mud), and the fate of an introduced test contaminant (⁷⁴As) were explored as part of a larger study of the feasibility of using microcosms for assessing the probable fate and effects of contaminants in natural ecosystems. An inoculum of local pond algae with attendant organisms was introduced into each microcosm. Substrate type influenced chemical and biological conditions and arsenic distribution profoundly, while size had lesser effects which were probably due to differences in surface area to volume ratio. Lake sediment contributed to significantly greater algal productivity as reflected by biomass, pH, dissolved oxygen, dissolved nutrients, and chlorophyll-a. Most of the arsenic moved into the mud of the lake sediment microcosms, but remained in the water of the sand microcosms. Bioaccumulation ratios for algae ranged from 370 for 7-L sand microcosms to 4300 for lake mud microcosms. Arsenic concentrations in snails were directly proportional to substrate arsenic concentrations. Transport of arsenic in the microcosms was in good agreement with published field data. The results of the experiment emphasized the importance of selecting components for test microcosms from the specific environments most likely to incur introduction of a particular contaminant.Research supported by theEnvironmental Protection Agency under Interagency Agreement No. IAGD60713, with theEnergy Research and Development Administration, Oak Ridge National Laboratory. Publication No. 1058,Environmental Sciences Division, ORNL.Operated byUnion Carbide Corporation for theEnergy Research and Development Administration.     

Microcosm Evaluation of the Toxicity and Risk to Aquatic Macrophytes from Perfluorooctane Sulfonic Acid

Perfluorooctane sulfonic acid (PFOS) is an anthropogenic contaminant detected in various environmental and biologic matrices. This compound is a fluorinated surfactant, a class of molecules renowned for their persistence and their global distribution but for which few ecotoxicological data are currently available, especially under field conditions. The toxicity of PFOS to the aquatic macrophytes Myriophyllum sibiricum and M. spicatum was investigated using 12,000 L outdoor microcosms. Replicate microcosms (n=3) were treated with 0.3, 3, 10, and 30 mg/L PFOS as the potassium salt and assessed at regular intervals during a period of 42 days. M. sibiricum was more sensitive to PFOS under these simulated field conditions than M. spicatum. Toxicity was observed in the evaluated end points at >3 mg/L PFOS for EC₁₀s and >12 mg/L PFOS for EC₅₀s for M. spicatum and in M. sibiricum at >0.1 mg/L PFOS for EC₁₀s and >1.6 mg/L PFOS for EC₅₀s. The no observed–effect concentration (NOEC) for M. spicatum was consistently 11.4 mg/L PFOS, whereas the NOEC for M. sibiricum was 0.3 mg/L PFOS. A risk assessment for these plants estimated a negligible probability of toxicity being observed in these plants from PFOS exposure at current environmental concentrations.     

An Assessment of Five Australian Polychaetes and Bivalves for Use in Whole-Sediment Toxicity Tests: Toxicity and Accumulation of Copper and Zinc from Water and Sediment

The suitability of two polychaete worms, Australonereis ehlersi and Nephtys australiensis, and three bivalves, Mysella anomala, Tellina deltoidalis, and Soletellina alba, were assessed for their potential use in whole-sediment toxicity tests. All species except A. ehlersi, which could not be tested because of poor survival in water-only tests, survived in salinities ranging from 18 to 34 during the 96-hour exposure period. No mortality was observed in any of the species exposed to sediment compositions ranging from 100% silt to 100% sand for 10 days, thus demonstrating the high tolerance of the five species to a wide range of sediment types. All species showed decreased survival after exposure to highly sulfidic sediments in 10-day whole-sediment tests. In 96-hour water-only tests, survival decreased, and copper accumulation in body tissues increased with exposure to increasing copper concentration for all species except A. ehlersi, which again could not be tested because of its poor survival in the absence of sediment. S. alba and T. deltoidalis were the most sensitive species to aqueous copper (LC50s of 120 and 150 g Cu/L, respectively). All species tested were relatively insensitive to dissolved zinc up to concentrations of approximately 1,000 g/L. In addition and with the exception of N. australiensis, all species accumulated significant levels of zinc in their body tissues. Whole-sediment tests were conducted over a 10-day period with copper-spiked (1,300 g/g) and zinc-spiked (4,000 g/g) sediments equilibrated for sufficient time to ensure that pore water metal concentrations were well below concentrations shown to have any effect on organisms in water-only tests. Survival was decreased in the bivalves T. deltoidalis and S. alba after exposure to copper-spiked sediments, and all species—except T. deltoidalis, in which 100% mortality was observed—accumulated copper in their tissues. Exposure to zinc-spiked sediments significantly decreased the survival of only one species, T. deltoidalis. Both polychaetes appeared to regulate concentrations of zinc in their body tissues with no significant uptake of zinc occurring from the sediment phase. Of the five species assessed in this study, T. deltoidalis was found to be the most sensitive to copper- and zinc-contaminated sediments, and based on commonly used selection criteria (ASTM 2002a, ASTM 2002b, ASTM 2002c) is recommended for development as test species in whole-sediment toxicity tests.     

Effects of diflubenzuron on benthic macroinvertebrates in littoral enclosures

Two applications of the insect growth regulator diflubenzuron were made to replicate littoral enclosures at nominal concentrations of 0.7, 2.5, 7.0, and 30 g/L. Assessment of the effects of this insecticide on benthic macroinvertebrate community structure was accomplished by measuring changes in abundance and taxonomic richness. Chironomidae and Ephemeroptera were the most sensitive groups sampled, with no observed effect concentrations of 2.5 and 0.7 g/L, respectively. No adverse effects were observed on Mollusca or Oligochaeta at any of the test concentrations. Taxonomic richness was noticably reduced at 7.0 and 30 g/L on all post-application sampling dates, producing changes in community structure that persisted for 57 days.     

Metal Concentrations and Responses of Chironomid Larvae Exposed to Thailand Pulp and Paper Mill Effluent

Pulp and paper mills (PPM) may discharge insufficiently treated waste into rivers and give rise to serious effects with aquatic life. This study investigated the biological response of the chironomid (Chironomus javanus, Kieffer) when exposed to PPM effluent. Effluent concentrations of BOD, COD, TKN, TS, Cr, Cu, Pb and Zn were high. Cd and Cr concentrations in chironomid were the most accumulated. Whole effluent toxicity on the chironomid test organism was significant as expressed by the percent survival and decreased with increasing concentration. Highest dry weight, head capsule and length of the chironomid test organism corresponded to 100% effluent at a specific time. Effect of dilution was assessed by using glutathione S-transferase activity on chironomid and corresponded to 6.25% effluent during 48–96 h which was significantly increased in the chironomid. The results showed that the chironomid was sensitive to PPM effluent and toxicity tests can be used for assessing the effect of effluent on aquatic species.     

The Effects of an Herbicide and Antibiotic Mixture on Aquatic Primary Producers and Grazers

Widespread use of agrochemicals increases their likelihood of entering aquatic systems in mixture. Despite different modes of action, atrazine (herbicide) and tetracycline (antibiotic) adversely affect non-target photosynthetic organisms individually, but the effects of simultaneous exposure to both contaminants are untested. We created microcosms containing microalgae (Chlorella sp.), floating macrophytes (Lemna minor), and a zooplankton grazer (Daphnia magna). Microcosms were exposed to environmentally relevant concentrations of atrazine and tetracycline, alone and together, for 10 days. Atrazine decreased Chlorella sp. abundance, but not enough to reduce food availability to D. magna whose reproduction and mortality were unaffected. In contrast, tetracycline and atrazine appeared to have additive effects on L. minor abundance and growth inhibition. These additive adverse effects suggest increased potential for L. minor population decline over the long term, and potential for altered species interactions in aquatic systems receiving agricultural runoff.