Μg Litre Research Articles

Effects of microcystin-LR and cyanobacterial crude extracts on embryo-larval development of zebrafish ( Danio rerio)

Eggs of zebrafish ( Danio rerio) were exposed to microcystin-LR at concentrations of 0.5, 5 and 50 μg litre −1 from blastula stage up to the end of embryonic development. No effects were observed during this period. After termination of exposure and transfer into microcystin-LR-free water, the evaluation at the end of the larval period showed decreased survival at 5 and 50 μg litre −1 microcystin-LR. Furthermore, concentrations of 0.5, 5 and 50 μg litre −1 microcystin-LR retarded larval growth. Far more pronounced effects occurred following exposure with various aqueous cyanobacterial crude extracts from field samples and batch cultures: gross malformations and high mortalities during embryonic development were observed.

Toxicity of cyanide and cyanide complexes to the marine diatom Nitzschia closterium

The effect of sodium cyanide (NaCN), iron-cyanide complexes and a blast furnace effluent on the growth of the unicellular marine diatom Nitzschia closterium was investigated. Due to the volatile nature of HCN, the free and total cyanide concentrations in all test solutions were monitored daily to ensure that average daily losses of free cyanide did not exceed 5%. The iron-cyanide complexes were less toxic than the NaCN, with 72-h EC 50 values of 57, 127 and 275 μg total-CN litre −1 for NaCN, K 3Fe(CN) 6 and K 4Fe(CN) 6, respectively. The estimated lowest observed effect concentration (LOEC) for NaCN was 10 μg litre −1. The toxicity of the cyanide complexes was largely due to free cyanide (HCN + CN −) with possible additional toxicity caused by dissociation of the complexes at the algal cell membrane. The toxicity of an effluent from a blast furnace drawdown episode also correlated well with the toxicity of free cyanide.

Detection and Quantification with 16S rRNA Probes of Planktonic Methylotrophic Bacteria in a Floodplain Lake

Two approaches employing 16S rRNA oligonucleotide probes, in situ hybridization combined with 33P-autoradiography and 32P-labeled slot-blot hybridizations on nitrocellulose filters, were used to enumerate methylotrophic bacteria in the water column of Ryans 1 Billabong, a small floodplain lake in northeastern Victoria, Australia. Methylotrophic bacterioplankton numbered 0.6–1.2 × 109 cells liter−1 in the winter of 1994, and 0.8–5.5 × 109 cells liter−1 in the summer of 1994–95. This was equivalent to 10–46% of total bacterioplankton cell counts, determined via epifluorescence microscopy. Methylotrophic bacteria were not detected in the water column of the nearby Kiewa River, and a set of laboratory controls indicated that the high abundance of methylotrophs in the billabong samples was not a methodological artifact. There was no change, with water depth, in total bacterioplankton or methylotroph abundance in winter, a result consistent with the water column being well mixed at this time of year (dissolved O2 concentrations 5–7 mg liter−1; dissolved methane concentrations 45 cm; dissolved methane concentrations 500 μg liter−1 near the sediments) and there was a correspondingly marked increase in the abundance of total bacterioplankton and methylotrophs with depth. In situ hybridizations and slot-blot hybridizations both indicated that type II methylotrophs (detected with a probe specific for the 9-α subgroup of Proteobacteria) were markedly less abundant than were type I and X methylotrophs (detected with a probe specific for the 10-γ subgroup of Proteobacteria).

A red-tide bloom of Chattonella antiqua (Raphidophyceae) in the Seto Inland Sea, Japan, in 1987 analysed as changes in photosynthetic pigments determined by high-performance liquid chromatography

A severe red-tide bloom of Chattonella antiqua (Raphidophyceae) was observed in the Seto Inland Sea (Japan) in summer 1987. The C. antiqua bloom was monitored from beginning to end at the 0, 5, 10, 15 m and bottom layers of a fixed sampling station almost every two days. Carotenoids and chlorophyllous pigments were measured by reversed-phase high-performance liquid chromatography before and during the bloom. Before the C. antiqua bloom, some diatoms were dominant, with a chlorophyll a (Chl a) concentration ranging between 2 and 8 μg litre −1 at the surface. The maximum Chl a concentration reached 27 μg litre −1 at the surface during the bloom, this being due to C. antiqua. Violaxanthin, which is a constituent carotenoid of C. antiqua, varied in line with cell concentration of the species. The relative abundance of C. antiqua was estimated as its Chl a contribution to total Chl a; the Chl a contributions of Raphidophyceae, Bacillariophyceae and Dinophyceae were calculated from pigment ratios obtained by multiple regression analysis of pigment concentrations. The relative abundance of C. antiqua at the surface was calculated to be 0–16% before the bloom and 83–100% during the bloom.

Persistence of tebufenozide in aquatic ecosystems under laboratory and field conditions

The persistence and dissipation behaviour of tebufenozide, an ecdysone agonist, were investigated: (1) under laboratory conditions in aquatic models set up in glass aquaria, and (2) under field conditions in in-situ aquatic enclosures deployed in a mixed-wood boreal forest lake. Two models were set up in the laboratory study (Study I), which was conducted at constant conditions of temperature, water pH and photoperiod. In Model I, partitioning of tebufenozide from sediment, treated at a concentration of 1400 μg kg -1 , into untreated water was examined. The results showed that the chemical moved very little from the treated sediment into water. The concentration in sediment and water decreased gradually during the 90-day incubation period. Tebufenozide disappeared faster from the top layer of sediment than from the middle and bottom layers. The half-lives of disappearance were 64 days for the top layer but >90 days for the middle and bottom layers respectively. In Model II, partitioning from water, treated at a concentration of 350 μg litre -1 , into untreated sediment was investigated. The results showed that the chemical moved from treated water into sediment due to adsorption. Little vertical downward movement of the adsorbed residues from the top layer of sediment occurred into layers beneath. The adsorbed residues were also not released readily back into water. The concentration in water and sediment decreased gradually during the 90-day incubation period. The half-life of dissipation from water was 67 days. The field microcosm study (Study II), conducted under fluctuating conditions of temperature, water pH and photoperiod, involved application of tebufenozide onto aquatic enclosures at four concentrations of 0.05, 0.10, 0.26 and 0.5 mg litre -1 . This study also showed that the chemical moved downwards from the applied location and was adsorbed onto sediment. The chemical persisted longer in Study II than in Study I. Tebufenozide, being photo-labile, probably degraded faster after constant exposure to light in Study I than after exposure to fluctuating light in Study II. At 90 days after treatment in Study I, only about 55% of the applied material persisted in the sediment, and there was little accumulation. In Study II, the material not only persisted but also was accumulated in the sediment, since at 92 days post-treatment the residues were about 25 times higher than the applied concentration level. Residues in water also decreased more rapidly in Study I than in Study II, because the concentration at 90 days post-treatment was about 41% of the applied value. In Study II, however, about 65% of the applied chemical persisted in water at 92 days post-treatment. While the long persistence of tebufenozide in both the laboratory and field studies was attributable to its low vapour pressure, low water solubility, high octanol/water partition coefficient etc., the differences in the persistence characteristics observed in the two studies were due to the fluctuating environmental conditions and water pH encountered in the field study, compared with the constant environmental conditions and water pH utilized in the laboratory study.

Seasonal fluctuations and diurnal oscillations in nitrate of a heathland brook

A 5-year study on nitrogen dynamics were performed in a pristine heathland catchment (2.55 km 2) in southern Norway. The catchment received 1.6 g total N m −2 yr −1 from wet and dry deposition, which is nearly tenfold more than that of northern Norway. Compared to most Norwegian catchments and forested areas, there is only a modest depression in mid-summer nitrate in runoff from winter maxima of nearly 250 μg litre −1 to late summer minima of 50–100 μg NO 3-N litre −1. N:P-ratios in runoff was strongly skewed towards P-limitation, and concentrations of both phosphate and total-P were normally below detection limits (<1 μg litre −1). The nitrate response of a three days P-enrichment in late May in the main brook draining the area was monitored continuously with a 10-min resolution for two months. The data confirmed a strong P-limitation and revealed a strong nitrate uptake and diurnal oscillations in nitrate concentrations over a period of more than one month following the P-enrichment. Over this period, mid-day concentrations were reduced by a factor of 2–3 relative to night maxima. Such reductions in nitrate during day relative to night-time may have profound effect on transport or budget estimates based on day-time samples only. Nitrate contributed normally 20–30% to anion acidity, and over the summer period there was a significant negative correlation between nitrate concentrations and pH, suggesting that increased N-uptake could also affect pH of such low-alkalinity systems.

Aflatoxins and their Metabolites in the Tissues, Faeces and Urine from Lambs Feeding on an Aflatoxin-Contaminated Diet

Twenty-four lambs were intoxicated with 2.5 mg of aflatoxin (AF) kg -1 in their feed for 21 days. Twelve lambs were slaughtered at day 21 and the remaining animals had an 8 day clearance period. Aflatoxins and their metabolites were detected in liver, kidneys, faeces and urine using TLC and fluorescence densitometry. During the intoxication period, the samples gave a wide range of concentrations, the lower extreme being in the liver and the kidney (0.03 μg kg -1 of AFG 1 ) and the higher extreme in faeces (61.82 μg kg -1 of AFM 1 ) and urine (27.84 μg litre -1 of AFM 1 ). The average value of AFB, (1.94 ± 0.9 μg kg -1 ) was higher than AFM 1 (0.35 ± 0.17 μg kg -1 ) in the liver. In the kidney AFM 1 (5.45 ± 4.01 μg kg -1 ) was higher than AFB 1 (1.29 ± 0.84 μg kg -1 ). There were higher concentrations of AFM 1 (27.2 ± 16.1 μg kg -1 , 7.37 ± 6.53 μg litre -1 , respectively, of average level) in faeces and urine, than of AFB 1 (17.25 ± 8.1 and 1.78 ± 1.57 μg litre -1 , respectively). AFB 2a appeared in the kidney (0.05 ± 0.03 μg kg -1 ) and urine (0.35 ± 0.25 μg litre -1 ). The clearance time of AFB 1 from the faeces was less than or equal to 8 days and in all samples aflatoxin residues were still detected on the 8th day of the clearance period although in low quantities. These results suggest that aflatoxin transfer to and elimination by the liver and the renal tissue is small and that the danger to humans consuming lamb meat is also small. The examination of the faeces and urine could be useful as markers to detect lambs consuming a contaminated diet.

Laboratory effects of microcosm size and the pesticide chlorpyrifos on benthic macroinvertebrate colonization of soft estuarine sediments

A 42-d flow-through experiment was conducted to evaluate the effects of the organo-phosphate pesticide, chlorpyrifos, and microcosm size (small: 144 cm 2; large: 400 cm 2) on benthic estuarine macroinvertebrate colonization. Nested central and perimeter (outside margin) cores were used to assess animal distribution within microcosms. Fine-grained, organically-rich (approximately 4.0% organic carbon and 20% dry wt) sediments were nominally fortified with chlorpyrifos controls, low (1.0) and high treatments (10.0 μg −1 wet sediment). Large microcosms contained a significantly (p < 0.05) higher average taxa richness (10.9) than small microcosms (8.6) but small microcosms contained a significantly greater average animal density (295.8; numerical abundance adjusted to unit area) than large microcosms (120.5). Density of the polychaete, Neanthes succinea, the amphipod, Corophium acherusicum, and the barnacle, Balanus sp., was significantly greater in small microcosms but density of Ensis minor was significantly greater in large microcosms. In small and large microcosms, respectively, densities averaged significantly greater numbers in perimeter cores (e.g. 203.1 and 75.1) vs central cores (71.9 and 45.4). Average density decreased significantly with increasing chlorpyrifos concentration from controls (326.8), to low (123.8) and high (78.8) treatments. The density decrease was significantly related only to C. acherusicum whose densities decreased from controls (285.8) to low (88.5) and high (43.9) dosed microcosms. Application of an equilibrium partitioning model indicated that density of C. acherusicum was sensitive to an estimated interstitial water concentration of approximately 0.48 μg liter −1. Non-metric multidimensional scaling ordination analyses provided important insights into response patterns not available through ANOVA procedures. A permutation procedure (ANOSIM) detected a significant size effect ( p < 0.0001) and a significant effect between controls and low ( p < 0.042) and high doses ( p < 0.013) but not between low and high chlorpyrifos treatments ( p < 0.465). A single species, C. ascherusicum, as in the ANOVA analyses, dominated contributions to community average percent dissimilarity in most combinations of microcosm size and chlorpyrifos treatment effects (range: 8.4–21.9%). Community structure differed significantly in several combinations of microcosm size, core position and chlorpyrifos treatment. Results confirm earlier work that intrinsic design factors influence benthic macroinvertebrate community structure and determine taxa available to pesticide exposure in microcosms.

Relative importance of iron and molybdenum in restricting phytoplankton biomass in high phosphorus saline lakes

Eleven prairie saline (conductivity 1.8–58.8 mS cm−1) lakes were examined over the 1994 growing season to determine what salinity-related factor or factors were responsible for controlling phytoplankton standing crops. The study lakes were characterized by high total P (0.15–24.2 mg liter−1), total N (3.75–12.35 mg liter−1), total Fe (55–2,800 µg liter−1), dissolved organic C (40–195 mg liter−1), pH and alkalinity, but comparatively low (usually <100 µg liter−1) dissolved inorganic N. Chlorophyll a (Chl a) concentrations in all but the two least saline lakes were relatively low (20 µg liter−1), up to three orders of magnitude below those predicted by freshwater P-based models. High alkaline phosphatase activities (APA) and rapid 32PO4 (orthophosphate) uptake indicated that the two least saline lakes were P limited; these lakes had seston deficient in P, N, and protein. APA and 32PO4 uptake were below detection in the more saline lakes (conductivity >3 mS cm−1), indicating P sufficiency; seston from these lakes was deficient in N but not protein. Nitrogen-fixing cyanophytes were important only in one of the lakes examined. Nutrient addition bioassays indicated that phytoplankton biomass was not limited exclusively by inorganic N availability, nor by a combination of Mo and N. For water from all but one of the P-sufficient lakes, addition of Fe to bioassays resulted in a remarkable increase in Chl a concentrations. Addition of Fe and Mo had the same effect as that of Fe alone, while the most saline lake appeared to be limited by one or more additional trace elements (but not Mo). Reducing the alkalinity of the bioassay water stimulated growth in the same manner as the Fe additions, suggesting that the bioavailability of the (largely particulate) Fe already present was severely restricted by lake-water alkalinity. Some component of lake-water alkalinity (which increased with conductivity in these lakes) appears to be the key factor limiting Fe bioavailability and restricting phytoplankton standing crops in the higher salinity lakes.

Patterns in phytoplankton taxonomic composition across temperate lakes of differing nutrient status

We describe the relationships between summer average total phosphorus (TP) and the biomass of six major phytoplankton taxonomic groups from 91 north temperate lakes. Both regression and a locally weighted smoothing (LOWESS) analyses show that all groups increase with TP but over different nutrient ranges. At nutrient extremes, i.e. very low and high levels of TP, the few taxonomic groups that dominate total biomass are generally dissimilar. In oligotrophic and eutrophic lakes, most group biomass curves show corresponding increases or decreases, but different rates of change. The curves converge at intermediate TP levels (∼10–30 µg liter−1) where there is increased equitability among algal groups. In highly eutrophic lakes, the slope of the total biomass curve decreases, as do all the relative abundances of all groups except blue-greens and diatoms. We conclude that the curvilinearity of the TP-total biomass curve is not attributable to a single taxonomic group, because all groups show some nonlinearity in relation to TP. We suggest that morphological diversity, differential herbivory, and, in particular, mixing regime may explain some of the observed patterns.

Plasma and Tissue Thyroxine and Triiodothyronine Contents in Sublethally Stressed, Aluminum-Exposed Brown Trout (Salmo trutta)

Immature female brown trout,Salmo trutta,were exposed to pH 5.0 soft water in the presence or absence of aluminum (Al) at 12.5 μg liter−1and their plasma concentrations and tissue contents of thyroxine (T4) and triiodothyronine (T3) were compared with those of a control group of trout held in pH 7.0 soft water. After 120 hr, plasma cortisol, glucose, T4, and T3concentrations were greater in the Al-exposed trout than in trout exposed to acid conditions alone, indicating that although the Al conditions were sublethal, a significant stress response was elicited. Significant increases in liver T4content, liver 5′-monodeiodinase activity and liver T3content indicated increased hepatic T4to T3conversion in the Al-exposed trout. The T4contents of brain, gill filaments, white muscle, heart ventricle, caudal kidney, and ovary were not significantly altered by Al exposure. The T3content of caudal kidney and ovary were significantly lower in Al-exposed trout than in control fish in neutral water but were unchanged in the brain, gill filaments, heart ventricle, and white muscle of these trout. The present data support previous observations of increased plasma T3concentrations in sublethally Al-exposed brown trout and indicate that at least part of the increased plasma T3concentration is due to an increased hepatic uptake of T4and monodeiodination to T3. However, analysis of nonhepatic tissue T3content gave no indication of increased T3production by these tissues.

The induction of metallothionein in tissues of the Norway lobster Nephrops norvegicus following exposure to cadmium, copper and zinc: The relationships between metallothionein and the metals

Nephrops norvegicus were exposed simultaneously to cadmium, copper and zinc over an 18-day period. Exposure concentrations were control, 1, 5 and 25 μg litre −1 for cadmium and copper and 8, 40 and 200 μg litre −1 for zinc. Concentrations of cadmium, copper, zinc and metallothionein were measured in homogenates of both the gill and the hepatopancreas. Quantification of metallothionein was carried out by differential pulse polarography. Cadmium concentrations increased significantly in the gill and hepatopancreas of both male and female animals in response to increases in exposure concentration. In contrast, the concentration of copper and zinc increased significantly in the gills of males, but not in females. In the hepatopancreas, neither copper nor zinc resulted in significant changes in concentrations of these metals. Metallothionein concentrations in the gill and hepatopancreas were increased significantly in relation to metal exposure in both males and females. Concentrations of cadmium and metallothionein in both the gill and hepatopancreas of males and females were positively correlated. Copper in the hepatopancreas also showed positive relationships with MT concentrations in males, but not in females. This study suggested that cadmium MTs in the gill and hepatopancreas of Nephrops norvegicus could be used as a sensitive tool to detect cadmium contamination in the lobsters, although this was not true for copper and zinc.

Toxicity of acid-sulphate soil leachate and aluminium to the embryos and larvae of Australian bass (Macquaria novemaculeata) in estuarine water

The toxicity of leachate water from acid-sulphate soil to the early life stages of Australian bass, Macquaria novemaculeata, incubated in seawater was evaluated. Acid-sulphate soil leachate water (pH≥6.8) delayed the hatching of fertilised eggs, but after 48 h the per cent hatching was normal. In comparison, acidic saline water (25‰ salinity) at pH 4.0 or less prevented embryos from hatching. The survival of yolk-sac larvae exposed to acid-sulphate soil leachate water at a concentration of 32% in seawater and an initial pH of 7.2, was significantly different to controls after 96 hours. In corresponding tests with only acidified saline water (20‰ salinity), pH levels equal to or below 5.0 killed yolk-sac larvae after 96 h exposure. Aluminum showed a pH dependent toxicity to yolk-sac larvae, with added aluminium as low as 200 μg litre−1 having a significant effect on larval survival at pH 5.5, and concentrations of 600–800 μg litre−1 having a significant effect on larval survival at an initial pH range of 6.0 < pH < 6.8. It was concluded that significant mortality of the early life stages of Australian bass would occur if they are exposed to acid-sulphate soil leachate that results in a pH in the receiving estuarine water below 5.5, or when the pH is below 6.8 and aluminium is present at a total concentration of 800 μg litre−1 or greater.

Effects of lead-contaminated surface water from a trap and skeet range on frog hatching and development

Pickerel frogs (Rana palustris) and bullfrogs (Rana catesbeiana) were exposed from the egg stage to lead-contaminated surface water from a trap and skeet range. Seven experimental treatments were employed: 25, 50, 75 and 100% range water, 100% range water plus a chelating agent (sodium citrate), control water and control water plus chelating agent. Total lead concentrations in 100% range water treatments varied from 840–3150 μg litre −1, with the filterable form accounting for approximately 4–5% of the total. Hatching was not affected in either species ( p > 0.2). There were highly significant differences in mortality among treatments for R. palustris ( p = 0.0001), with tadpoles exhibiting 100 and 98% mortality after 10 d of exposure to 100 and 75% range water, respectively. Mortality in the 100% range water + citrate treatment was similar to controls ( p > 0.05). There were no significant differences in mortality among treatments for R. catesbeiana after 10 d of exposure ( p = 0.7119). Exposure to lead in the range water did not adversely affect the growth of surviving R. palustris or R. catesbeiana tadpoles after 14 weeks and 10 weeks, respectively. In both species, the intestinal mucosa in tadpoles exposed to range water was reduced in thickness. Scanning electron micrographs of R. palustris tadpoles that died in 100% range water revealed stunted tail growth, incurvation of the spine, hydropsy and generally reduced body size.

Changes in gill morphology of Atlantic salmon ( Salmo salar) smolts due to addition of acid and aluminum to stream water

One-year-old Atlantic salmon smolts were held in three artificial channels adjacent to a softwater (mean sp. cond. 30 μS cm −1, circumneutral stream. Water in one channel was untreated (mean pH 6.25); the others received additions of acid (to mean pH 5.6), or acid plus aluminum (to mean pH 5.5; mean exchangeable Al 158 μg litre −1). Gills were sampled after 16 and 23 days of exposure for morphometric examination. On primary lamellae, chloride cells were more numerous in both experimental treatments than in controls. In contrast, numbers of chloride cells on secondary lamellae were elevated only in fish exposed to acid without added Al. Chloride cell size and shape also varied with time and treatment. Fewer gill mucous cells were found in fish exposed to acid plus Al than in controls. Chloride cell proliferation and structural changes may represent an attempt to compensate for increased ionic effluxes with low pH stress by increasing uptake. However, if Al concentrations are high, chloride cells do not proliferate along the secondary lamellae, or proliferating cells are damaged and lost. This may limit the potential to increase ionic uptake.

A Scanning Electron Microscope Investigation of the Effects of Pollutants on the Hepatopancreatic Ceca ofGammarus pulex(L.)

Scanning electron microscope studies were performed on the peripheral muscle network (myoepithelium) of the hepatopancreatic ceca ofGammarus pulex(L.) exposed to lindane, copper, or 3,4-dichloroaniline (3,4-DCA) for a 24-hr period. The structural integrity of the myoepithelium of gammarids from control and test treatments was assessed using semiquantitative techniques. The lowest observed effect concentrations for structural changes were determined as 29.8 μg liter−1lindane, 55 μg liter−1copper, and 8.7 mg liter−13,4-DCA. The sensitivity of the bioassay and the significance of the morphological changes observed in the hepatopancreatic ceca ofG. pulexare discussed.

Factors regulating phytoplankton and zooplankton biomass in temperate rivers

By measuring Chl a, zooplankton biomass, nutrient concentrations, and water residence time in 31 rivers in eastern Canada, we tested the following hypotheses: Chl a is positively related to nutrient concentrations and water residence time, and zooplankton biomass is positively related to Chl a and water residence time. Chl a ranged from 1.8 to 27.6 µg liter−1, total phosphorus (TP) from 7.3 to 212.3 µg liter−1, and water residence time from 3.3 to 19.4 d. There was a positive relationship between Chl a and TP (R2 = 0.76) and no relationship between Chl a and residence time. In contrast, zooplankton biomass was positively related to water residence time (R2 = 0.33). There was only a weak positive relationship between Chl a and zooplankton biomass. Mean river zooplankton biomass was low (11.3 µg liter−1 dry mass) compared to lakes of similar Chl a concentration.

Preferential Flow Pathways and Their Capacity to Transport Isoproturon in a Structured Clay Soil

A field experiment was established to monitor preferential flow pathways and their capacity to transport isoproturon in a heavy clay soil. A hydrologically defined plot of 600 m2 at a field site on the Oxford University Farm at Wytham was created with integral flow monitoring and sampling devices. Data are presented from two flow events which occurred in April and May 1994. The highest concentrations of isoproturon (130 μg litre−1) were observed in the drainage system. The vast majority of the 0·7% of applied pesticide that left the plot was via the drainage system (75–90%) with lateral subsurface flow accounting for a smaller proportion (max 23%). Whilst high pesticide concentrations could be found in overland-flow water, the volumes of water moved by this route were small (max 3%). Less water was estimated to have left the field in response to rainfall than in the previous year. This was attributed to decay of the mole drain system. Consequently the amount of applied pesticide lost in runoff (0·7%) was less than that estimated for the first year (1·5%). The work has shown that, even when a farmer follows best practice in the application of a herbicide to a winter cereal in a drained clay field, high concentrations of the herbicide (relative to the EC drinking water limit) will contaminate surrounding watercourses.

Preferential Flow Pathways and Their Capacity to Transport Isoproturon in a Structured Clay Soil

A field experiment was established to monitor preferential flow pathways and their capacity to transport isoproturon in a heavy clay soil. A hydrologically defined plot of 600 m2 at a field site on the Oxford University Farm at Wytham was created with integral flow monitoring and sampling devices. Data are presented from two flow events which occurred in April and May 1994. The highest concentrations of isoproturon (130 μg litre−1) were observed in the drainage system. The vast majority of the 0·7% of applied pesticide that left the plot was via the drainage system (75–90%) with lateral subsurface flow accounting for a smaller proportion (max 23%). Whilst high pesticide concentrations could be found in overland-flow water, the volumes of water moved by this route were small (max 3%). Less water was estimated to have left the field in response to rainfall than in the previous year. This was attributed to decay of the mole drain system. Consequently the amount of applied pesticide lost in runoff (0·7%) was less than that estimated for the first year (1·5%). The work has shown that, even when a farmer follows best practice in the application of a herbicide to a winter cereal in a drained clay field, high concentrations of the herbicide (relative to the EC drinking water limit) will contaminate surrounding watercourses.

Action of Cypermethrin on Tissue Transamination during Nitrogen Metabolism inCyprinus carpio

Freshwater fish,Cyprinus carpio,was exposed to sublethal concentration (3 μg liter−1) of cypermethrin for 5 and 10 days to examine the changes in the transamination process during the formation of nitrogenous end products in four functionally different tissues, namely, gill, liver, brain, and muscle. Increases in total and soluble protein contents were noticed in all the tissues of exposed fish with a decrease in free amino acids and protease activity. Activity levels of both the transaminases, aspartate aminotransferase and alanine aminotransferase, and glutamate dehydrogenase were elevated, indicating active transamination and oxidative deamination. Attenuation of ammonia was consistent in both treatment groups. However, urea level decreased at the 5-day exposure period but increased by Day 10, manifesting the conversion of toxic ammonia to urea. Glutamine content was consistently raised upon exposure to the toxicant. In support of this, increases in glutamine synthetase and suppression of glutaminase were noticed. It clearly indicates that ammonia is not stored in the tissues in spite of active oxidative deamination when the fish is in a polluted environment. All the observations made demonstrate that the fish has adopted more than one compensatory mechanism during the process of transamination of nitrogenous products.