Respective LC50s Research Articles

Genotoxic assessment of cerium and magnesium nanoparticles and their ionic forms in Eisenia hortensis coelomocytes by alkaline comet assay.

The present study aimed to evaluate the genotoxic potential of cerium oxide (CeO2 ), magnesium oxide (MgO) nanoparticles and their ionic forms by alkaline comet assay. Eisenia hortensis were exposed to different series of concentrations (25, 50, 100, 200, and 400 μg/ml) of chemicals for 48 h to find LC50 . The LC50 for MgO and CeO2 NPs were 70 and 80 μg/ml. Whereas, the LC50 for their ionic forms were 50 and 70 μg/ml. To assess the potential DNA damage caused by the chosen chemicals, E. hortensis was further exposed for 48 h to the following concentrations, based on their respective LC50s : LC50/2 , LC50 , and 2xLC50 . Comet scores demonstrated the significant increase (p < 0.05) in DNA damage at all concentrations, both for NPs and ionic forms in a concentration-dependent manner. Findings of the present study revealed the genotoxic effects of CeO2 NPs, MgO NPs and their ionic forms on E. hortensis. RESEARCH HIGHLIGHTS: Genotoxic assessment of CeO2 and MgO NPs and their ionic forms was conducted. Characterization of NPs through electron microscopy and alkaline comet assay was performed on E. Hortensis. Highest DNA damage of CeO2 and MgO NPs was observed on earthworm.

Acute and chronic toxicity of neonicotinoid and butenolide insecticides to the freshwater amphipod, Hyalella azteca

Neonicotinoids are the most widely used insecticides in the world. They are preferentially toxic to insects while displaying a low toxicity toward vertebrates, and this selective toxicity has resulted in the rapid and ubiquitous use of these compounds. However, neonicotinoids have been detected in agricultural surface waters and are known to cause adverse effects in non-target aquatic organisms. A wide range of toxicity has been reported for aquatic crustaceans, but most of the studies focus on the acute effects of imidacloprid, and few data are available regarding chronic effects of other neonicotinoids or neonicotinoid replacements (e.g., butenolides). The objective of this study was to assess the acute and chronic toxicity of six neonicotinoids (imidacloprid, thiamethoxam, acetamiprid, clothianidin, thiacloprid, and dinotefuran) and one butenolide (flupyradifurone) to the freshwater amphipod Hyalella azteca. Chronic (28-d), water-only, static-renewal tests were conducted. Survival was assessed weekly, and growth was measured at the end of the exposure. Effects of neonicotinoids varied depending on the compound. Acute (7-d) LC50s were 4.0, 4.7, 60, 68, 230, and 290 μg/L for clothianidin, acetamiprid, dinotefuran, thiacloprid, imidacloprid, and thiamethoxam, respectively. Chronic (28-d) survival and growth were reduced at similar concentrations to acute (7-d) survival for thiamethoxam, acetamiprid, clothianidin, and dinotefuran. However, chronic survival and growth of amphipods exposed to imidacloprid and thiacloprid were reduced at lower concentrations than acute survival, with respective 28-d LC50s of 90 and 44 μg/L, and EC50s of 4 and 3 μg/L. Flupyradifurone was intermediate in toxicity compared to the neonicotinoids: 7-d LC50, 28-d LC50, and 28-d EC50 were 26, 20, and 16 μg/L, respectively. The concentrations of imidacloprid and clothianidin reported for North American surface waters fall within the effect ranges observed in this study, indicating the potential for these compounds to cause adverse effects to indigenous populations of H. azteca.

Sublethal Effects of vATPase-A and Snf7 dsRNAs on Biology of Southern Corn Rootworm, Diabrotica undecimpunctata howardi Barber.

RNA interference is a powerful tool against corn rootworm. Adults and neonates of southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), were exposed to the LC50 of vATPase-A and Snf7 double-stranded RNAs (dsRNAs), and the effects on female fecundity, egg viability, male fitness as measured by sperm viability and mating capacity, larval recovery along with dry weight, and instar determination 10 d after exposure to dsRNA, were determined. Significant reductions were observed for a number of parameters in dsRNA-exposed rootworms relative to control treatments. Female fecundity and larval recovery were significantly reduced after exposure to both dsRNAs. In addition, larval dry weight and recovery of 2nd and 3rd instars along with dry weight for 3rd instars were significantly reduced after neonate exposure to vATPase-A dsRNA. Neither dsRNA affected male capacity to mate or sperm viability after exposure to the respective LC50s. After 10 d of feeding on untreated corn roots, neonates that survived exposure for 2 d to the vATPase-A dsRNA LC50 exhibited lower dry weight than the control. There was significant gene knockdown in adult males and females after exposure for 5 d to LC50 of vATPase-A and Snf7 dsRNAs. The parameters are discussed in terms of fitness and possible outcomes after deployment of corn hybrids expressing dsRNAs.

Efficacy of spray applications of entomopathogenic fungi against western flower thrips infesting greenhouse impatiens under variable moisture conditions

Laboratory bioassays of three entomopathogenic fungi (Beauveria bassiana strain GHA, Metarhizium brunneum strain F52, and Metarhizium anisopliae s.l. strain ESC-1) were conducted against 2nd-instar nymphs of Frankliniella occidentalis. All three fungi were highly virulent, with respective LC50s of 193, 140, and 72conidia/mm2 of treated leaf surface. Efficacy tests were conducted against thrips infesting small plots of Impatiens walleriana on open greenhouse benches under variable moisture conditions. Multiple spray applications of fungal conidia suspended in 0.01% Silwet® were made at a high rate of 2×1014conidia/ha at 3–5-day intervals, and efficacy was assessed from twice-weekly samples of both flowers and foliage. During tests, moisture conditions were modified via controlled sprays of water onto the concrete floor beneath the greenhouse benches for a period of ca. 40h (from the evening through the second night) following each application (post-spray period). Efficacy of the pathogens expressed as percent reduction of the combined populations of thrips nymphs and adults relative to spray-carrier controls was ultimately correlated to greenhouse environmental conditions. Mean relative humidity (RH) over all test days was a strong predictor of thrips control on foliage (R2=0.820) and flowers (R2=0.756). Fungal efficacy was most strongly and consistently predicted by moisture conditions during the post-spray periods. The single best predictor was mean number of hours during post-spray periods when RH was ⩾80% (R2 foliage=0.834; R2 flowers=0.908). The three fungi produced similar levels of thrips control under comparable moisture conditions. Maintenance of 80% RH for ca. 25h during post-spray periods resulted in >70% control of thrips in foliage. Substantially longer periods of high humidity (35h) were required to achieve comparable control in flowers. Control⩾70% in both foliage and flowers prevented pest populations from increasing. Aspects of the impatiens crop that create a challenge for thrips control using fungal entomopathogens are described and discussed.

Acute toxicity of sodium bicarbonate, a major component of coal bed natural gas produced waters, to 13 aquatic species as defined in the laboratory

Water produced during coal bed natural gas (CBNG) extraction in the Powder River Structural Basin of Wyoming and Montana (USA) may contain concentrations of sodium bicarbonate (NaHCO3) of more than 3000 mg/L. The authors evaluated the acute toxicity of NaHCO3, also expressed as bicarbonate (HCO3(-)), to 13 aquatic organisms. Of the 13 species tested, 7 had a median lethal concentration (LC50) less than 2000 mg/L NaHCO3, or 1300 mg/L HCO3(-). The most sensitive species were Ceriodaphnia dubia, freshwater mussels (Lampsilis siliquoidea), pallid sturgeon (Scaphirhynchus albus), and shovelnose sturgeon (Scaphirhynchus platorynchus). The respective LC50s were 989 mg/L, 1120 mg/L, 1249 mg/L, and 1430 mg/L NaHCO3, or 699 mg/L, 844 mg/L, 831 mg/L, and 1038 mg/L HCO3(-). Age affected the sensitivity of fathead minnows, even within life stage. Two days posthatch, fathead minnows were more sensitive to NaHCO3 and HCO3(-) compared with 4-d-old fish, even though fish up to 14 d old are commonly used for toxicity evaluations. The authors recommend that ion toxicity exposures be conducted with organisms less than 24 h posthatch to ensure that experiments document the most sensitive stage of development. The results of the present study, along with historical and current research regarding the toxicity of bicarbonate, may be useful to establish regulatory standards for HCO3(-). This article is a US Government work and is in the public domain in the USA.

Comparison of arsenate and cadmium toxicity in a freshwater amphipod ( Gammarus pulex)

Cadmium is largely documented on freshwater organisms while arsenic, especially arsenate, is rarely studied. The kinetic of the LC50s values for both metals was realized on Gammarus pulex. Physiological [i.e. metal concentration in body tissues, bioconcentration factor (BCF)] effects and behavioural responses (via pleopods beats) were investigated after 240-h exposure. Arsenate LC50 value was 100 fold higher than Cd-LC50 value after 240-h exposure, while concentrations in gammarids were similar for both metals at their respective LC50s. BCF decreased with increasing cadmium concentration while BCF remained stable with increasing arsenate concentration. Moreover, BCF was between 148 and 344 times lower for arsenate than cadmium. A significant hypoventilation was observed for cadmium concentrations exceeding or close to the 240h-LC50 Cd, while gammarids hyperventilated for the lowest arsenate concentrations and hypoventilated for the highest arsenate concentrations. We discussed the relationships between potential action mechanisms of these two metals and observed results.

Comparative virulence of Beauveria bassiana isolates against lepidopteran pests of vegetable crops

Forty-three isolates of the entomopathogenic fungus Beauveria bassiana were screened for virulence against second-instar larvae of diamondback moth ( Plutella xylostella) (DBM), European corn borer ( Ostrinia nubilalis) (ECB), corn earworm ( Helicoverpa zea) (CEW), and fall armyworm ( Spodoptera frugiperda) (FAW); 30 of these isolates were tested against beet armyworm ( Spodoptera exigua) (BAW). Highly virulent isolates were also tested against black cutworm ( Agrotis ipsilon) (BCW), and the most virulent isolate was also assayed against imported cabbage worm ( Pieris rapae) (ICW) and cabbage looper ( Trichoplusia ni) (CL). All lepidopteran species tested were susceptible to B. bassiana. Corn earworm and beet armyworm were most susceptible to fungal infection, and fall armyworm was least susceptible. Limited testing suggested low susceptibility of black cutworm and cabbage looper. B. bassiana isolate 1200 exhibited virulence against all pest species greater than or equal to commercial strain GHA of B. bassiana currently registered in the USA as BotaniGard®. In assays in which larvae were topically sprayed and maintained on the treated substrate for 24 h at 100% relative humidity, 6-day (25 °C) median lethal concentrations (LC 50s) of this isolate against CEW, BAW, DBM, FAW, ICW, ECB, CL, and BCW were 4, 5, 7, 11, 12, 98, 125, and 273 conidia/mm 2, respectively. The respective LC 50s of commercial strain GHA against these pest species were 9, 67, 97, 1213, 29, 1668, 541, and 3504 conidia/mm 2. Use of LC 50 versus median lethal concentration ratios (comparing LC 50s of each isolate to a “standard” strain) generated similar rankings of isolate virulence. Results from parametric ANOVAs of log LC 50 values followed by Tukey HSD multiple comparisons tests and those from Kruskal–Wallis nonparametric analyses followed by sequential Bonferroni tests for means comparisons were nearly identical.

Erufosine, a novel alkylphosphocholine, in acute myeloid leukemia: single activity and combination with other antileukemic drugs

PurposeAlkylphosphocholines represent a new class of cytostatic drugs with a novel mode of action. Erufosine (ErPC3), the first compound of this class that can be administered intravenously, has recently been shown to be active against human tumor and leukemic cell lines.MethodsIn order to evaluate the antileukemic potential of ErPC3 in acute myeloid leukemia (AML) the lethal concentration 50% (LC 50) was determined using WST-1 assay. For analysis of cell death, staining for Annexin V and activated caspase 3 was performed. An interaction analysis was performed by calculation of combination index and construction of isobolograms.ResultsThe LC 50 was 7.4 μg/ml after 24 h and 3.2 μg/ml after 72 h in HL 60 cells and 30.1 and 8.6 μg/ml, respectively, in 19 fresh samples from patients with AML. ErPC3 was found to be cytotoxic in HL60 cells with distinct activation of caspase 3. ErPC3 was not cross-resistant with cytarabine, idarubicine and etoposide as shown by the linear relation of respective LC 50s. The latter agents, however, exerted an additive cytotoxicity in combination with ErPC3 as revealed by isobologram analysis and combination index, although results are uneven for idarubicine.ConclusionBased on these data ErPC3 appears as a novel antileukemic candidate drug, which needs to be explored further in the treatment of AML.

Baseline toxicity of Cry1A toxins to the spotted bollworm, Earias vittella F.

The baseline toxicity of Cry1A toxins on seven field populations of Earias vittella (Fab.) was determined through log dose probit analysis. In almost all populations tested the spotted bollworm larvae were found to be extremely susceptible to all the three Cry1A toxins. Results indicated that the three Cry toxins tested against neonates were very effective in the nanogram range. The LC 50s for Cry1Aa ranged from 0.332 to 1.608 ng/sq.cm. of treated leaf. Cry1Ab exhibited an LC 50 in the range of 0.167 to 0.751 while LC 50 to Cry1Ac ranged from 0.280 to 1.215 ng/sq. cm. The data from all assays were pooled together and subjected to probit analysis to obtain a composite log dose response. The LC 50 deduced from the data were 0.59, 0.47 and 0.88 ng/sq cm, for Cry1Aa, Cry1Ab and Cry1Ac, respectively. This data would be useful to consider the respective LC 50s as the baseline susceptibility index for resistance monitoring through the conventional log dose probit assays. The LC 99 values deduced from the composite data were 446, 291 and 627 ng/sq cm, for Cry1Aa, Cry1Ab and Cry1Ac respectively. These values represent the diagnostic doses for routine monitoring of resistance to the respective toxins through discriminating dose assays.

Effects of heavy metals on the survival ofDiacypris compacta (Herbst) (Ostracoda) from the Coorong, South Australia

The hypermarine southern Coorong is threatened by proposals to drain relatively fresh surface water and groundwater from adjacent agricultural areas into the Coorong. These influent waters carry moderate loads of heavy metals. Acute toxicity of heavy metals toDiacypris compacta, an abundant ostracod in the Coorong, was measured in the laboratory at 18°C in a static system using Coorong water (pH 7.8 salinity 50 ppt). At 4 days (96 h) the mean values of LC50 for copper, zinc, lead and, cadmium respectively were 0.8, 2.1, 3.1 and 4.3 mg L−1, and at 8 days the respective mean LC50s were 0.4, 0.7, 2.2 and 1.1 mgL−1. The effect of two or three metals on mortality was additive in some cases and synergistic in other cases, but generally less than additive. However, in all cases mortality was greater in the presence of two or three metals than in the presence of a single metal. According to ANZECC (1992) guidelines, maximum acceptable concentrations of heavy metals should be no higher than 0.01 x the lowest LC50 value. Using the lowest LC50 values forDiacypris compacta obtained at 8 days, maximum acceptable concentrations in the Coorong would be 4, 5, 9 and 22 μgL−1 for copper, zinc, cadmium and lead respectively, the values for zinc and copper failling below those recommended by ANZECC (1992) for marine waters. Reported concentrations of copper and zinc in surface water and groundwater in areas adjacent to the Coorong sometimes exceed these values, hence drainage of these waters into the Coorong represents a significant hazard to the Coorong biota.

Chronic effects of low insecticide concentrations on freshwater caddisfly larvae

The insecticide load in surface waters does not ordinarily reach concentrations acutely toxic to aquatic fauna. The effects of the low insecticide concentrations typical of natural habitats are still not clear, for they often appear only after relatively long exposure times. To test such a situation, the insecticides lindane and parathion were introduced into a static-with-renewal outdoor aquaria system at concentrations about four and five orders of magnitude lower than their respective 96-h LC50s, and their chronic (about 90 days) effects on the survival rate of freshwater caddisfly larvae were observed. The emergence and hence survival rate of Limnephilus lunatus Curtis was significantly reduced by lindane at 0.1 ng l−1, a value nearly five orders of magnitude lower than the 96-h LC50. Parathion, with acute and subacute toxicity similar to that of lindane, did not significantly alter the emergence rate of this species. In contrast, this substance did produce a significant reduction in emergence rate of the closely related species Limnephilus bipunctatus Curtis at 1 ng l−1, even though this species was significantly less susceptible than L. lunatus to parathion at high concentrations. We conclude that chronic insecticide exposure can be hazardous to freshwater macroinvertebrates even at unexpectedly low concentrations. The low-concentration effects may depend on both species and substance and therefore cannot be predicted from toxicity data at higher concentrations.

Interpreting aquatic toxicity QSARs: the significance of toxicant body residues at the pharmacologic endpoint

Aquatic QSAR investigations employ bioassay data where a biological response is associated with a toxicant concentration in the exposure water. Although convenient this ignores the fundamental principle that the response is more closely related to an amount present in the organism. This problem has been examined using acute toxicity and bioconcentration QSARs employing log K ow as the molecular descriptor. Combining these QSAR relationships enables estimates of the amount of toxicant in organisms to be made. For acute narcosis (50% mortality) the toxicant level in the hydrophobic (lipid) phase of an exposed organism is, as a first approximation, constant at ∼ 50mmoll −1 of lipid. For the acute toxicity of a variety of hydrophobic narcotic organics examined by US EPA-Duluth in tests with fathead minnows, this corresponds to a whole-body residue of about 4 mmol kg −1. Although the level in the hydrophobic phase remains constant, for hydrophilic chemicals (log K ow < 1.5) the contribution of the hydrophilic (water) phase of the organism dominates and total body residues should be similar to the respective threshold LC 50s. This has important implications in simple pharmacokinetic modelling and in interpreting residue levels in organisms collected in environmental monitoring studies.

Acute toxicity of permethrin or glyphosate pulse exposure to larval white sucker (catostomus commersoni) and juvenile flagfish (jordanella floridae) as modified by age and ration level

AbstractA factorial design was used to determine the effects of age (2, 4, and 8 d for flagfish; 13, 20, and 26 d for white sucker) and ration (fed or unfed) on the acute toxicity of permethrin pulse exposure. A similar design was used to evaluate the acute toxicity of glyphosate to flagfish. Relative tolerance was assessed by determining the 2‐h pulse‐exposure concentration causing 50% mortality (PE LC50) over the subsequent 96 h. Age at exposure and the presence or absence of food modified the toxicity of permethrin to both flagfish and white sucker. White sucker were consistently less tolerant of permethrin than flagfish. Fed and unfed 8‐d‐old flagfish, as well as unfed 2‐d‐olds, showed equivalent levels of permethrin tolerance, with respective 96‐h PE LC50s of 0.57, 0.54, and 0.68 mg L−1. They were significantly less tolerant than 4‐d‐old unfed juveniles (2.97 mg L−1), which were in turn significantly less tolerant than 2‐ and 4‐d‐old fed juveniles, whose respective 96‐h PE LC50s were 5.55 and 7.91 mg L−1. Unfed white suckers were less tolerant than fed white suckers at all ages tested. Unfed white suckers at 13 d (96‐h PE LC50, 0.002 mg L−1) and 20 d (0.001 mg L−1) were significantly less tolerant than unfed fish at 26 d (0.172 mg L−1) and fed fish at 13 d (0.184 mg L−1), which were more tolerant than 20‐d‐old fed fish (0.010 mg L−1). Fed fish at 26 d of age were the most tolerant (3.668 mg L−1). Glyphosate proved to be relatively nontoxic to flagfish up to 30 mg L−1. No mortality was observed during the bioassays with 2‐ and 4‐d‐old fed and starved fish. Fed 8‐d‐olds (96‐h PE LC20, 29.6 mg L−1) were significantly more tolerant of glyphosate than were unfed 8‐d‐olds (96‐h PE LC20, 2.94 mg L−1). The sharply delineated periods of permethrin sensitivity are discussed with reference to the theory of saltatory ontogeny.

Acute Toxicity of Ammonia and Nitrite to Spotted Seatrout

Abstract Median lethal concentrations (LC50) of ammonia and nitrite were determined for spotted seatrout (Cynoscion nebulosus) in static tests. Ammonia toxicity tests were conducted with eggs, larvae hatched from eggs previously exposed to ammonia (ammonia-exposed eggs), larvae hatched from eggs not previously exposed to ammonia (unexposed eggs), 1-month-old juveniles, and 4-month-old juveniles. Nitrite toxicity tests were conducted with eggs and larvae. Spotted seatrout eggs were the life history stage most tolerant of un-ionized ammonia; 91.6% hatch occurred at 6.0 mg NH3-N/L. The 24-h LC50 for larvae hatched from both ammonia-exposed and unexposed eggs was 0.28 mg NH3-N/L. The 24-h LC50 of nitrite for larvae was 980 mg NO2-N/L; 92% hatch occurred at 1,200 mg NO2-N/L. Tolerance of un-ionized ammonia increased with age through the 4-month juvenile stage; the respective 24-h NH3-N LC50s for 1 - and 4-month-old juveniles were 1.38 and 1.98 mg/L, and the respective 96-h LC50s were 0.98 and 1.72 mg/L.

Acute Toxicity of Methoxychlor to Larval White Sucker (Catostomus commersoni) as Modified by Age, Food Availability, and Egg Preexposure

Methoxychlor is currently pulsed into several western Canadian rivers at 0.30 mg∙L−1 to control the emergence of blackflies (Diptera: Simuliidae). A 2-h exposure of white sucker (Catostomus commersoni)) eggs to 4.83 mg methoxychlor∙L−1 at 1, 3, or 6 d postfertilization increased the incidence of deformities in both 1-d-old and pooled 3- and 6-d-old eggs (2.9 and 3.1%, respectively) compared with control eggs(1.1%). Larvae from exposed eggs showed a 2-d delay in the onset of exogenous feeding. Exposure as eggs increased methoxychlor tolerance. Respective 168-h PE LC50s (the 2-h pulse-exposure concentration causing 50% mortality over 168 h) for 2-d-old larvae from control eggs and eggs exposed for 2 h to methoxychlor at 1, 3, or 6 d postfertilization were 0.36, 1.04, 2.05, and 2.67 mg∙L−1 Methoxychlor toxicity in control larvae was modified by age; 10-d-old larvae were less tolerant than 2-, 18-, and 26-d-old larve, with respective PE LC50s of 0.04, 0.36, 0.34, and 0.20 mg∙L−1. After the onset of feeding, food availability modified toxicity. The96-h PE LC50sfor 18-d-oldfedand unfed larvae and 26-d-old fed and unfed larvae were 0.34, 0.032, 0.20, and 0.038 mg∙L−1, respectively. Swimbladder development was arrested in 2-d-old larvae exposed for 2 h to 0.10 mg methoxychlor∙L−1 at 9 d of age. White sucker survival may be at risk in methoxychlor-treated rivers.

The effects of polychlorinated biphenyls (Aroclors 1016 and 1254) on mortality, reproduction, and regeneration in Hydra oligactis.

Budding and tentacle regeneration were observed inHydra oligactis following exposure to the commercial PCB mixtures Aroclor 1016 and 1254. The acute toxicity of these PCB s was also compared by determining their respective 72-hr LC50s. The animals were exposed to the PCBs as a component of an artificial pond water medium with PCB dilutions being made from a 49:1, reagent grade acetone:PCB solution. All exposures were continuous with the medium being replaced daily. Animals used in studying the effects of these chemicals on tentacle regeneration had their heads transected at the time of initial exposure to the PCBs. Observation were taken at 24, 48, 72, and 96-hr of incubation at 19 ±0.2°C.