The Influence of Salinity and Dissolved Organic Carbon on the Toxicity of Copper to the Estuarine Copepod, <Emphasis Type="Italic">Eurytemora affinis</Emphasis>

The objectives of this study were to determine the influence of salinity (2.5, 5, 15, and 25 ppt) at dissolved organic carbon (DOC) concentrations of 1.3–3.3 mg/L and DOC concentrations of 2, 4, 6, and 8 mg/L at a fixed salinity of 10 ppt on the acute toxicity (96-h LC50s) of copper to the sensitive estuarine copepod, Eurytemora affinis. For both salinity and DOC experiments, various other chemical constituents such as DOC, Ca²⁺, Cl^-, Mg²⁺, Na⁺, K⁺, SO₄^2-, hardness, alkalinity, salinity, pH, temperature, and dissolved oxygen were measured at selected copper concentrations at test initiation and test termination. Dissolved copper, copper speciation, and organic copper complexation were measured at various test conditions during the salinity and DOC experiments. Ninety-six-hour dissolved copper LC50 values for the four salinities ranged from 58 μg/L (25 ppt) to 104 μg/L (5 ppt) with intermediate values of 71 μg/L (2.5 ppt) and 68 μg/L (15 ppt). The 58, 68, and 71 μg/L LC50 values were not significantly different. Copper LC50 values at 5 ppt were higher than at both 15 and 25 ppt. The isosmotic salinity of E. affinis is approximately 5–10 ppt, which was a likely factor for why the LC50 value increased for copper at 5 ppt. The dissolved copper 96-h LC50s for E. affinis increased from 76 to 166 μg/L as DOC increased from 2 to 8 mg/L. This result is not surprising and is consistent with reported values for other saltwater species.     

Sublethal Effects of Three Pesticides on Larval Survivorship, Growth, and Macromolecule Production in the Aquatic Midge, Chironomus tentans (Diptera: Chironomidae)

Effects of long-term exposure to each of three pesticides including atrazine, DDT, and chlorpyrifos on larval survivorship, growth, and macromolecule (total body protein and RNA) production were evaluated in the aquatic midge, Chironomus tentans, under laboratory conditions. Newly hatched larvae were exposed to atrazine at 30 and 150 μg/L, DDT at 0.01 and 0.05 μg/L, or chlorpyrifos at 0.02 and 0.10 μg/L throughout one life cycle. Larval survivorship was evaluated at 20 d and the end of the test, and larval growth at 20 d. Chlorpyrifos at 0.1 μg/L reduced the midge survivorship by 67% after 20-d exposure. However, neither atrazine nor DDT affected larval survivorship. The ash-free dry weight of midge larvae exposed to chlorpyrifos at 0.1 μg/L was 1.5-fold greater than that of the control whereas neither atrazine nor DDT showed a significant effect on the ash-free dry weight. In addition, exposures of midges to chlorpyrifos at 0.1 μg/L increased the adult emergence rate by 81% as compared to the control although the actual number of adults that emerged from chlorpyrifos-treated larvae was significantly decreased. Both the increased ash-free dry weight of larvae and increased adult emergence rate were likely caused by reduced competition for both food and space among the survivors due to increased larval mortality. Although neither total protein nor total RNA production was significantly affected in larvae exposed to each pesticide for 20 d, a significantly higher number of males over females (ratio = 4) emerged from midges exposed to DDT at 0.05 μg/L. Our study indicates that chronic exposure to low concentrations of chlorpyrifos and DDT results in significant mortality of midge larvae and alteration of the sex ratio of adult emergence, respectively. Because midges are important components of the food web, our results suggest that effects elicited directly or indirectly by long-term pesticide exposures may potentially disrupt both food chains and community structure in aquatic environments.     

The influence of salinity on the chronic toxicity of atrazine to an estuarine copepod: Implications for development of an estuarine chronic criterion

The goal of this study was to determine the influence of a range of salinities (5, 15, and 25 ppt) on the chronic toxicity of atrazine to the copepod, Eurytemora affinis during 8-day life-cycle tests. Survival, development (proportion of immature organisms) and reproduction (percent of egg-carrying females) were the endpoints used to determine chronic toxicity. Survival was the most sensitive endpoint and was therefore used to determine chronic values. The No Observed Effect Concentration (NOEC) and the Lowest Observed Effect Concentration (LOEC) at 5 ppt were 12.25 and 17.5 mg/L, respectively. The calculated chronic value was 14.6 mg/L. The NOEC and LOEC at 15 ppt were 17.5 and 25 mg/L, respectively, and the calculated chronic value at 15 ppt was 20.9 mg/L. The NOEC and LOEC at 25 ppt were 4.2 and 6.0 mg/L, respectively, while the calculated chronic value at 25 ppt was 5.01 mg/L. Results from a bootstrapping statistical technique demonstrated that there was a significant difference (p<0.05) between chronic values at 5 ppt (14.6 mg/L) and 25 ppt (5.01 mg/L), and between 15 ppt (20.9 mg/L) and 25 ppt (5.01 mg/L). There was no significant difference between chronic values at 5 ppt (14.6 mg/L) and 15 ppt (20.9 mg/L). These specific data for atrazine have important implications for development of estuarine water quality criteria, as toxicity test results at one salinity are not representative of the salinity range found in many estuaries.     

Application of a Benthic Euryhaline Amphipod, Corophium sp., as a Sediment Toxicity Testing Organism for Both Freshwater and Estuarine Systems

The use of an as-yet-undescribed euryhaline Corophium sp. amphipod as a sediment toxicity testing organism was assessed. The species was found to be ubiquitous in many tidal areas of the Hawkesbury River catchment. The salinity of habitat sites ranged from 0.1 to 24 ppt, sediment total organic carbon (TOC) ranged from 0.4% to 3.5%, and the fines content (< 63 μm particle size) of the sediment ranged from 4.3% to 47.6%. Monitored populations ranged from a density of 59 to 6622 individuals per m², with freshwater sites with a sediment fines content greater than 20% having the highest population densities. The sensitivity of the Corophium sp. was assessed by using copper chloride and ammonium chloride as reference toxicants in a 96-h static water-only test and a 10-day static sediment test. The LC50 for copper in freshwater-only exposures was 80 to 86 μg/L, using adult animals collected from the field. In contrast, the LC50 for copper in freshwater sediment and the sediment pore water were 840 mg/kg (dry weight) and 99 μg/L, respectively. The LC50 for ammonia (total) in freshwater-only at pH 7 was 5.5 mg/L. In contrast, the LC50 for ammonia (total) in freshwater sediment and the sediment pore water were 110 mg/kg (dry weight) and 6 mg/L, respectively. Laboratory cultures of 5‰ to 15‰ salinity were optimal for supporting the release of juveniles. Juveniles collected from laboratory cultures had a LC50 for copper in 5‰ and 10‰ salinity of 9 μg/L and 28.5 μg/L, respectively, in water-only exposures. The juveniles would be suitable for use in the development of a chronic sediment toxicity test with growth as the endpoint. Received: 21 February 1997/Accepted: 27 May 1997     

Life-Cycle Toxicity of Bis(Tributyltin) Oxide to the Sheepshead Minnow (Cyprinodon variegatus)

The effects of tributyltin (TBT) to the life cycle of the estuarine fish Cyprinodon variegatus were examined in a 180-day flow-through exposure. The study was initiated with embryos less than 24 h postfertilization and monitored through hatch, maturation, growth, and reproduction under continuous exposure to mean measured TBT concentrations of 5.4, 3.2, 1.3, 0.66, and 0.41 μg TBT/L. Progeny isolated at the onset of reproduction by the parental generation (F₀) were monitored for survival as embryos, survival as fry/juveniles, and growth 30 days postisolation. TBT, at a concentration of 5.4 μg/L, significantly reduced embryo survival of the F₀ generation sheepshead minnows. By day 145 of the exposure, significant effects to the survival of this generation increased and included all test concentrations ≥0.66 μg/L. Survival of 0.66 μg/L was reduced 59% relative to control survival by termination of the F₀ generation. Growth of F₀ generation organisms as measured by standard length was significantly reduced only on day 90 at 3.2 μg/L, however no significant reductions of wet or dry weight related to treatment concentration were detected. Due to complete mortality of organisms exposed to 5.4 μg/L by study day 7, effects to fecundity and progeny were monitored at measured concentrations of 3.2, 1.3, 0.66, and 0.41 μg TBT/L. Fecundity, as measured by the production of viable eggs produced per female per day, was unaffected by any of the test treatments. All F₁ generation embryos isolated from treatment chambers into 3.2 μg/L died. Survival, standard length, wet and dry weight of the F₁ generation at the remaining treatment concentrations were unaffected. The results of this study indicate that exposure to TBT reduced survival of the F₀ generation sheepshead minnow and establishes the lowest observed effect concentration (LOEC) as 0.66 μg TBT/L, and the no observed effect concentration (NOEC) as 0.41 μg TBT/L for this species. Received: 17 August 1998/Accepted: 14 March 1999     

Salinity effects on the bioavailability of aqueous metals for the estuarine killifish Fundulus heteroclitus

Estuarine organisms experience varying salinity conditions on a daily and seasonal basis, and these fluctuations could influence the amount of metal accumulated from the aqueous phase. The present study experimentally assessed the role of salinity (0, 2, 6, 12, and 25 ppt) on the uptake of As, Cd, Cr, inorganic Hg [Hg(II)], and methylmercury (MeHg) into the euryhaline killifish (Fundulus heteroclitus) from the aqueous phase using gamma-emitting radioisotopes. Patterns of metal uptake as a function of salinity varied by metal. Chromium showed no relationship with salinity; Cd, which was most affected by salinity, showed an inverse relationship; and As, Hg(II), and MeHg uptake increased as salinity increased from 0 ppt to 25 ppt. Arsenic (salinities ≤ 6 ppt) and Cr were regulated by the fish, whereas Cd, Hg(II), and MeHg were not. Cadmium, Hg(II), and MeHg are chloro-complexed, increasing bioavailability for Hg(II) and MeHg, and reducing bioavailability for Cd. Concentration factors (CFs) were >1 at all salinities for Cd, Hg(II), and MeHg, indicating that the fish were more enriched in the metal than the surrounding water, whereas As and Cr CFs were <1 at all salinities. Uptake rate constants (k(u)s) were highest for MeHg (0.79-2.29 L g(-1) d(-1)), followed by Hg(II), Cd, Cr, and lowest for As (0.0004-0.0008 L g(-1) d(-1)). Tissue distribution of each metal was determined by dissections. Data for Cd showed that as salinity increased, the concentration of this metal increased in the viscera, whereas it decreased in the head and gills, suggesting that drinking to osmoregulate may account for a portion of Cd uptake from the aqueous phase in marine fish.     

Presence of Polycyclic Aromatic Hydrocarbons (PAHs) in Apple in Rural Terrains from Mexico City

This paper describes PAH concentrations in apple crops that are growing in rural terrains in Mexico City. The concentrations of individual PAHs showed great variability, there being low and high molecular weight compounds in dry (high molecular weight for Tlahuac 7.06 μg/g and Milpa Alta 3.96 μg/g) and wet months (high molecular weight for Tlahuac 11.25 μg/g and Milpa Alta 12.05 μg/g). Some PAHs indicators and cross plot ratios Ant/(Ant + Phe) and Flu/(Flu + Pyr) define fossil fuels and vegetation combustion as the source of contamination over the cuticle of the apples. It is likely that deposition (dry and wet) is the principal source o f contamination over the apple surface. This study reveals the presence of PAHs in apples due to the high air contamination of Mexico City.     

Salinity acclimation modulates copper toxicity in the sheepshead minnow, Cyprinodon variegatus

The sheepshead minnow (Cyprinodon variegatus) is able to withstand a wide range of salinities. Salinity acclimation involves physiological and biochemical changes, which may influence how organisms respond to a stressor. The present study investigated effects of salinity acclimation on subsequent Cu toxicity. In experiment 1, fish were acclimated to a hyposmotic, isosmotic, or hyperosmotic salinity for 14 d and then exposed at these salinities to 16.6 μM Cu(2+) for 12 h. Survival differed during this Cu challenge; fish acclimated to 2.5 ppt salinity were much more sensitive to Cu than those acclimated to 10.5 or 18.5 ppt seawater. In experiment 2, fish were exposed to 14.6 μM Cu(2+) for 6 h after the 14-d salinity acclimation. Whole-body Cu, whole-body Na, liver lipid peroxidation (LPO), liver catalase activity, and liver glucose levels were determined before and after Cu exposure. Prior to Cu exposure, the acclimation groups differed only for liver glucose levels, which were higher in the 2.5 ppt acclimated fish than in the others. These same 2.5 ppt acclimated fish were markedly affected by Cu, having increased whole-body Cu and liver LPO and decreased whole-body Na levels. Copper exposure had generally insignificant effects for the 10.5 ppt and the 18.5 ppt acclimated fish. This study showed that even in euryhaline fish, salinity acclimation can have a drastic effect on Cu toxicity.     

Lethal body residue of chlorophenols and mixtures of chlorophenols in benthic organisms

The lethal body residue (LBR) of a few chlorophenol congeners were measured in the oligochaete worm Lumbriculus variegatus, and the LBR of pentachlorophenol was measured also in a midge, Chironomus riparius larvae. LBR is defined as the concentration of the compound in the organism, on molar basis, to cause death, and the LBR₅₀ is defined as the calculated LBR value to cause a 50% mortality in population after a given time. Groups of 30 or 40 organisms were exposed to different chlorophenol concentrations in artificial soft fresh water to achieve differential mortality. Exposure times were either 24 h or 48 h. In addition to exposures with individual congeners, mixtures of chlorophenols were also tested. After each exposure, the surviving organisms were collected and the body burden of chlorophenols was measured by gas chromatography with electron capture detection. The measured body burden was related to the percent mortality in the group. The trichlorophenols and pentachlorophenol have a 48-h LBR₅₀ of 0.45–0.66 μmol/g wet weight in L. variegatus. The 48-h LBR₅₀ of pentachlorophenol for C. riparius was 0.15 μmol/g wet weight, indicating a slight difference in the sensitivity of these two species. The 48-h LBR₅₀ of 2,3,4,6-tetrachlorophenol is 0.91 μmol/g wet weight, and the value for 2,6-dichlorophenol is 1.2 μmol/g wet weight in L. variegatus. The 48-h LBR₅₀s of the chlorophenol mixtures ranged from 0.50 to 0.83 μmol/g wet weight, demonstrating an additive toxicity. Received: 13 August 2001/Accepted: 6 March 2002     

Influence of salinity and temperature on acute toxicity of cadmium toMysidopsis bahia Molenock

Acute toxicity tests were conducted to compare estimates of toxicity, as modified by salinity and temperature, based on response surface techniques with those derived using conventional test methods, and to compare effect of a single episodic exposure to cadmium as a function of salinity with that of continuous exposure.Regression analysis indicated that mortality following continuous 96-hr exposure is related to linear and quadratic effects of salinity and cadmium at 20°C, and to the linear and quadratic effects of cadmium only at 25°C. LC50s decreased with increases in temperature and decreases in salinity. Based on the regression model developed, 96-hr LC50s ranged from 15.5 to 28.0 g Cd/L at 10 and 30% salinities, respectively, at 25°C; and from 47 to 85 g Cd/L at these salinities at 20°C. Trimmed Spearman-Karber method used in analysis of a second data set yielded estimates at 20°C and 25°C comparable to those of multiple regression analysis. At 30°C, the 96-hr LC50 was <11 g/L.The relationship of median tolerance to cadmium concentration and exposure time was related to the interaction of both factors and independent of salinity between 10 and 30% at 25°C. The quadratic model predicts mortality of 50% following exposures of <12 hr to the highest concentration examined (92 g/L). For exposure durations of 16 and 24 hr, 50% mortality is predicted to occur at 78 and 56 g/Cd/L, respectively.Environmental Research Laboratory-Narragansett, RI, Contribution #950.     

Behavioral Responses to Atrazine and Diuron in Goldfish

Experiments were performed in goldfish to determine the effects of a short-term exposure (24 h) to atrazine or diuron (0.5, 5, 50 μg/L) on some behavior endpoints related to swimming and social activities. Observations were also made to assess the influence of such exposure on the behavioral responses of fish to the flow of a crude skin extract solution from conspecifics, active in social chemocommunication and producing alarm behaviors. Additive tests were run to check the behavioral responses of previously unexposed goldfish to the flow of a solution of atrazine- or diuron-contaminated water, at three concentrations (0.1, 1, 10 mg/L). Significant burst swimming reactions appeared in response to a 24-h exposure to atrazine, at the lowest concentration tested (0.5 μg/L). A 24-h exposure to 5 μg/L atrazine or diuron was found to induce various significant behavioral alterations in fish. At this concentration, both herbicides decreased grouping behavior and atrazine also increased surfacing activity. Herbicide-exposed fish showed a decreased grouping behavior during the flow of the skin extract solution. Sheltering was also decreased during the flow of the biological solution in fish exposed to atrazine. Moreover, fish exposed to diuron clearly displayed attraction responses to the flow of the skin solution. Previously unexposed fish showed a significant increase in burst swimming reactions in response to the flow of a solution of atrazine- or diuron-contaminated water, at all concentrations tested (0.1, 1, 10 mg/L). Furthermore, the diuron-contaminated flow was found to be significantly attractive at the highest concentration. These results indicate that a short-term exposure to a relatively low concentration (5 μg/L) of atrazine or diuron can affect various behaviors of fish not only directly but also indirectly by altering the chemical perception of natural substances of eco-ethological importance. In consideration of the basic role of olfaction in fish behavior, these results also emphasize the need for further developments on the possible effects of aquatic toxicants on olfactory-mediated behaviors. Received: 4 October 1997/Accepted: 25 March 1998     

Influence of salinity on copper and azide toxicity to larval topsmelt Atherinops affinis (Ayres)

Performance of a 7-d growth and survival toxicity test protocol using larval topsmelt, Atherinops affinis (Ayres), was evaluated for copper chloride and sodium azide at representative estuarine salinities. Results showed that topsmelt are amenable to toxicity testing at estuarine salinities ranging from 5 to 34 since control survival was 100% in all toxicity tests. Sensitivity to both toxicants increased at lower salinities, with the LC50s for copper ranging from 205 g/L at 34 to 44 g/L at 10, and those for sodium azide ranging from 54 mg/L at 34 to 7 mg/L at 5. Larval tissue osmolality decreased with increasing copper concentration relative to control fish. Copper uptake was not affected by changes in salinity. This suggests that increased sensitivity to copper was due, in part, to the increasing physiological challenge of osmoregulation. It is also possible that cupric ion concentration increased at lower salinities, resulting in reduced larval survival. It is hypothesized that increased sensitivity to azide at lower salinity was due to the interaction between azide toxicity and increasing osmotic challenge. A second experiment with azide showed that larval acclimation time did not affect the interaction between salinity and azide toxicity.     

Sublethal Effects of Three Pesticides on Activities of Selected Target and Detoxification Enzymes in the Aquatic Midge, Chironomus tentans (Diptera: Chironomidae)

Sublethal effects of three pesticides including atrazine (triazine herbicide), DDT (organochlorinated insecticide), and chlorpyrifos (organophosphate insecticide) on acetylcholinesterase (AChE), general esterase (GE), glutathione S-transferase (GST), and cytochrome P450 monooxygenase (P450) activities were evaluated in the aquatic midge Chironomus tentans. Exposures of midges to atrazine at 30 and 150 micrograms per liter (μg/L) for 20 d (i.e., from the first- to fourth-instar larvae) enhanced P450 O-deethylation activity by 12.5- and 15.5-fold, respectively, but did not significantly change AChE, GST, and GE activities. Similar exposures to DDT at 0.01 and 0.05 μg/L did not significantly affect AChE, GE, and P450 activities; however, DDT at 0.05 μg/L enhanced GST activity toward the substrate 1-chloro-2, 4-dinitrobenzene by 33.6%. Exposures of midges to chlorpyrifos at 0.10 μg/L for 20 d reduced AChE activity by 59.8%, and GE activities toward the substrates α-naphthyl acetate and β-naphthyl acetate by 30.7 and 48.8%, respectively. The reduced GE activities appear to be due to the inhibition of several esterases, particularly the one with a slow migration, by chlorpyrifos as demonstrated by non-denaturing polyacrylamide gel electrophoresis. Furthermore, exposure of midges to chlorpyrifos at 0.10 μg/L for 20 d enhanced the P450 O-deethylation activity by 3.3-fold although no significant effect was observed at 0.02 μg/L for the same enzyme. These results provide insights into the sublethal effects of these commonly detected pesticides in aquatic environments on important enzymes in aquatic midges.     

Occurrence of Antifouling Biocides in Sediment and Green Mussels from Thailand

Various antifouling biocides were surveyed in sediment and green mussels (Perna viridis) from the coastal area of Thailand. The concentrations of butyltin (MBT), dibutyltin (DBT), and tiributyltin (TBT) in sediment from Thailand were in the range of 1–293 μg kg⁻¹ dry wt., 1–368 μg kg⁻¹ dry wt., and 2–1246 μg kg⁻¹ dry wt., respectively. A higher concentration of TBT was observed in industrial areas, where many tankers and cargo ships sail and moor. Phenyltin (PT) compounds were not detected in most of the sampling sites. The concentrations of MBT, DBT, and TBT in green mussels from Thailand were in the range of 8–20 μg kg⁻¹ wet wt., 4–9 μg kg⁻¹ wet wt., and 4–45 μg kg⁻¹ wet wt., respectively. The concentration of TBT was high in an area where aquaculture practice is common. The detection frequencies of TPT were low. Representative booster biocides were surveyed in sediment. The detection frequencies of Sea Nine 211 were low (2/13). Furthermore, Sea Nine 211 concentrations in the detected samples were at values near the detection limit (0.051–0.094 μg kg⁻¹ dry wt.). Diuron was detected at the highest level among the booster biocides in the range of 0.07–25 μg kg⁻¹ dry wt. Irgarol 1051 was detected in the range of 0.03–3.2 μg kg⁻¹ dry wt., and concentrations of the degradation product’s M1 were 0.03–4.9 μg kg⁻¹ dry wt. Diuron and Irgarol 1051 showed higher concentrations in industrial areas and fishery sites, respectively. Diuron was only detected among green mussels in the range of <0.64–9.6 μg kg⁻¹ wet wt. The lower ratio of Diuron and Irgarol 1051 for TBT concentration suggests that TBT is still being used in Thailand.     

Impact of Atrazine on Chlorpyrifos Toxicity in Four Aquatic Vertebrates

Atrazine has been shown previously to potentiate chlorpyrifos toxicity in selected invertebrates. This study examined interactions of atrazine and chlorpyrifos in four aquatic vertebrates. Organisms were exposed to binary mixtures of atrazine and chlorpyrifos during toxicity bioassays. Inhibition of cholinesterase (ChE) enzyme activity and chlorpyrifos uptake kinetics were also examined with and without atrazine exposure. Atrazine alone did not affect organisms at concentrations up to 5000 μg/L; however, the presence of atrazine at 1000 μg/L did result in a significant increase in the acute toxicity of chlorpyrifos in Xenopus laevis. Mixed results were encountered with Pimephales promelas; some bioassays showed greater than additive toxicity, while others showed an additive response. No effect of atrazine on chlorpyrifos toxicity was observed for Lepomis macrochirus and Rana clamitans. Atrazine did not affect ChE activity or chlorpyrifos uptake rates, indicating that these toxicodynamic and toxicokinetic parameters may not be related to the mechanism of atrazine potentiation of chlorpyrifos toxicity. Based on the results of this study, it does not appear that a mixture toxicity of atrazine and chlorpyrifos at environmentally relevant concentrations presents a risk to the vertebrate organisms examined in this study.     

Bioaccumulation of Toxic Metals (Cd and Cu) by <Emphasis Type="Italic">Groenlandia densa</Emphasis> (L.) Fourr.

In this study, Groenlandia densa (L.) Fourr. (opposite-leaved pondweed), was exposed to prepared stock solution of cadmium and copper with 1.0, 3.0, 5.0 and 7.0 mg L⁻¹ concentration in certain periods (24, 48, 72 and 96 h) and changing amount of accumulation of plants in depending on time and concentration was measured by atomic absorption spectrophotometer. The results show that under experimental conditions, G. densa (L.) Fourr. proved to be a good accumulator of Cd and Cu. Removal of the metals from solution was fast in the first 4 days. The accumulation of Cd and Cu increased with the initial concentration and also with time. The highest concentrations of each trace element accumulated in opposite-leaved pondweed tissues were 1,955 μg Cd g⁻¹, 6,135 μg Cu g⁻¹ after 4 days. The maximum values of bioconcentration factor (BCF) were found for Cd and Cu 724 and 1,669, respectively. BCF values for Cd and Cu increased with time.     

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.     

Residues of Atrazine andN-deethylated Atrazine in water from five agricultural watersheds in Québec

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) andN-deethylated atrazine (2-chloro-4-amino-6-isopropylamino-s-triazine) were monitored (1974 and 1975) in five rivers which drained agricultural areas in the Yamaska river basin of Québec. Water samples were collected frequently from April to December each year from sites near the outflow of each river. The water samples were extracted with benzene, chloroform, or ethyl acetate and the extracts were analyzed by gas chromatography using a Hall electrolytic conductivity detector and an alkali-flame detector. Atrazine andN-deethylated atrazine residues ranged in concentration from 0.01 to 26.9 μg/L and <0.01 to 1.34 μg/L, respectively, over the monitoring period. The highest levels of atrazine were observed in July each year and they coincided with the herbicide spraying season in this region and with occasional heavy rainfall events. Discharges (kg/yr) of atrazine from the five rivers were related to corn-growing area in each watershed. Losses of atrazine ranged from 0.1 to 2.9% of the atrazine that was estimated to have been applied in each watershed.     

Accumulation and Regulation of Zinc in Daphnia magna: Links with Homeostasis and Toxicity

Zinc accumulation in Daphnia magna was investigated, and the results were linked to the previously established optimal concentration range for zinc and D. magna. It was observed that organisms cultured in this optimal range (300–600 μg Zn/L) contained 212 ± 57 to 254 ± 79 μg Zn/g dry weight. Lower and higher zinc contents were obtained after acclimation to previously established culture concentrations inducing deficiency and toxicity, respectively. The calculation of bioconcentration factors indicated that zinc was actively regulated, at least up to a concentration of 600 μg Zn/L. Zinc uptake and elimination are rapid processes; major increases and decreases in body content occurred within 1 day. Zinc concentrations in daphnids exposed to 600 μg Zn/L fluctuated with 2- to 3-day intervals, suggesting a role of molting in the regulation and elimination of zinc. Received: 12 November 2001/Accepted: 15 April 2002     

A Preliminary Study of the Distribution of Selected Trace Metals in the Besut River Basin,Terengganu, Malaysia

This paper presents a preliminary result carried out in the Besut River basin, Terengganu, Malaysia to determine the selected trace metal concentrations. Concentrations of dissolved Pb, Cu, and Fe during the present study were in the range of 3.3–8.3 μg/L Pb, 0.1–0.3 μg/L Cu, and 1.1–12.3 μg/L Fe. For the particulate fraction concentrations of Pb, Cu, and Fe ranged from 1.0 to 3.6 μg/L, 0.3 to 2.8 μg/L, and 114 to 1,537 μg/L, respectively. The concentrations of metals in this study area, in general, were lower than those reported for other study areas. Higher metal concentrations measured in the wet monsoon season suggest that the input was mainly due to terrestrial runoff.