Acute toxicity of widely used pharmaceuticals in aquatic species: Gambusia holbrooki, Artemia parthenogenetica and Tetraselmis chuii

Pharmaceuticals are continuously dispersed into the environment as a result of human and veterinary use, posing relevant environmental concerns. This study evaluated the acute toxicity of three therapeutic agents (diazepam, clofibrate, and clofibric acid) and a detergent (sodium dodecyl sulfate; SDS) in three aquatic species, namely the euryhaline fish Gambusia holbrooki, the hypersaline crustacean Artemia parthenogenetica, and the marine algae Tetraselmis chuii. The ranking of 50% lethal concentrations (LC50) for the two animal species and 50% inhibitory concentration (IC50) for the algal species was, in decreasing order, clofibric acid > SDS > diazepam > clofibrate for G. holbrooki, clofibric acid > clofibrate > SDS > diazepam for A. parthenogenetica, and clofibric acid > clofibrate > SDS > diazepam for T. chuii. These differences show that the intrinsic nature of test organisms must be considered when evaluating the toxicity of these agents to aquatic ecosystems.     

Mixture toxicity of the anti-inflammatory drugs diclofenac, ibuprofen, naproxen, and acetylsalicylic acid

The ecotoxicity of the nonsteroidal anti-inflammatory drugs (NSAIDs) diclofenac, ibuprofen, naproxen, and acetylsalicylic acid (ASA) has been evaluated using acute Daphnia and algal tests. Toxicities were relatively low, with half-maximal effective concentration (EC50) values obtained using Daphnia in the range from 68 to 166 mg L(-1) and from 72 to 626 mg L(-1) in the algal test. Acute effects of these substances seem to be quite improbable. The quantitative structure-activity relationships (QSAR) approach showed that all substances act by nonpolar narcosis; thus, the higher the n-octanol/water partitioning coefficient (log Kow) of the substances, the higher is their toxicity. Mixture toxicity of the compounds could be accurately predicted using the concept of concentration addition. Toxicity of the mixture was considerable, even at concentrations at which the single substances showed no or only very slight effects, with some deviations in the Daphnia test, which could be explained by incompatibility of the very steep dose-response curves and the probit analysis of the data. Because pharmaceuticals in the aquatic environment occur usually as mixtures, an accurate prediction of the mixture toxicity is indispensable for environmental risk assessment.     

Sensitivity of juvenile freshwater crayfish Cherax destructor (Decapoda: Parastacidae) to trace metals

Juvenile Cherax destructor was investigated as a potential test species for toxicity testing of trace metals in Australian freshwater systems. Adult male and female C. destructor were bred in the laboratory to obtain 4-week old juveniles, which were used in the toxicity tests. Animals were exposed to a range of concentrations of the trace metals ions copper (377-1275 microg/L), cadmium (377-1275 microg/L), nickel (300-1013 mg/L) and iron (36-168 mg/L) in static-renewal 96-h bioassays. The 96-h LC50 value for cadmium was 379, 494 microg/L for copper, 50 mg/L for iron and 327 mg/L for nickel demonstrating a decreasing toxicity of these metals to C. destructor. Comparison of LC50 values for metals for this species with those for other aquatic organisms reveals that C. destructor is less sensitive to trace metals than most other tested species.     

Effects of five rice herbicides on the growth of two threatened aquatic ferns

The effects of five rice herbicides bensulfuron methyl, mefenacet, quinoclamine, simetryn, and thiobencarb on the growth of two threatened aquatic ferns Azolla japonica and Salvinia natans were tested using 12-day exposure experiments at 0.1-100 nM which are expected to be present in drainages and rivers in Japan. As a reference species, Lenma minor was also used to examine the toxicity of bensulfuron methyl. Bensulfuron methyl had the most pronounced effect on the relative growth rate (RGR) of A. japonica, S. natans, and L. minor with an EC50 of 5.0, 0.54, and 10 nM, respectively. The other herbicides reduced the RGR of the aquatic ferns only at the highest concentration (100 nM) or not at all. S. natans showed the highest susceptibility to bensulfuron methyl among the three species, and the EC50 for this species was comparable to or below the maximum concentration (0.49-5.6 nM) that had been previously detected in 7 of 11 rivers in Japan. These results suggest that bensulfuron methyl runoff in drainages and rivers in Japan is expected to have adverse effects on the growth of threatened aquatic ferns in some cases, and that no or small effects occur for the other four herbicides tested.     

Aquatic toxicity of nitrogen mustard to Ceriodaphina dubia, Daphnia magna, and Pimephales promelas

Investigation of toxicity of mustard compounds to aquatic organisms has been limited although their effects on terrestrial mammal species have been well studied. In this study, the 48-h LC50 values of nitrogen mustard (HN2) are reported for two aquatic invertebrate species (Daphnia magna and Ceriodaphnia dubia) and for one fish species (Pimephales promelas). Mean LC50 values to C. dubia, D. magna, and P. promela were 1.12, 2.52, and 98.86 mg/L, respectively. C. dubia was the species most sensitive to HN2. Seven-day lethal and sublethal tests with P. promelas and C. dubia were also conducted. In chronic tests, fathead minnow growth was significantly reduced by 2.50 mg/L HN2, while C. dubia reproduction was significantly affected by 7.81 mug/L HN2. These adverse effects on aquatic organisms caused by lower-level concentrations of HN2 indicate that a possible aquatic ecosystem disaster could occur either after a chemical spill or during chemical warfare.     

<Emphasis Type="Italic">In Vitro</Emphasis> Biotransformation of Amitriptyline and Imipramine with Rat Hepatic S9 Fraction: Evaluation of the Toxicity with Spirotox and Thamnotoxkit F™ Tests

Pharmaceutical products, as well as their related metabolites, end up in the aquatic environment after use. Little is known about the effects and the hazard of exposure to drugs for aquatic organisms. This study was designed to assess the ecotoxicity of amitriptyline (AMI), imipramine (IMI), and their metabolites. The tested drugs were very toxic to the protozoan Spirostomum ambiguum and the crustacean Thamnocephalus platyurus with the LC50 values around 1 mg l⁻¹. Moreover, simple additivity occurs between the drugs and their N-desmethyl metabolites. Tested compounds were incubated with S9 rat hepatocyte fraction at 37°C for 4 hours. Unchanged drugs and metabolites were determined using high-pressure liquid chromatography–photodiode array detector. AMI and IMI were biotransformed almost completely. Three AMI and IMI metabolites were detected: desmethyl-, didesmethyl-, and N-oxide. The toxicity of the deproteinated reaction mixtures (TU) was compared to the toxicity equivalency units (TEU) calculated based on the concentrations of the drugs and their LC50 values. It has been demonstrated that the toxicity of mixture of metabolites to Spirotox and Thamnotoxkit F™ is higher than the predicted value calculated from the concentrations of the drugs and their N-desmethylated derivatives in the sample. The results indicate that the harmfulness of the drug metabolites should be taken into consideration in the ecotoxicological studies.     

Comparing the acute response to cadmium toxicity of nauplii from different populations of Artemia

The lethal responses to cadmium of instar II nauplii from eight populations of Artemia belonging to the species Artemia franciscana, Artemia salina, Artemia persimilis, and Artemia parthenogenetica have been compared. Generalized linear models were used to fit mortality. The model indicates that there is a relationship between species, type of population, and mortality rate. The two populations of A. franciscana were the most sensitive to cadmium toxicity (median lethal concentration, LC50, of 93.3-142 mg/L), while the population of A. persimilis was the most resistant (LC50 of 284 mg/L). Differences in the phenotypic variability in each population were assessed through the slope of the mortality curve, with A. persimilis exhibiting the highest diversity. This study suggests that habitat peculiarities and historical origin of the populations may have a significant influence on their response to cadmium toxicity.     

Effects of a brassinosteroid analogue to mosquito larvae

Many plant compounds are able to modulate herbivore growth and reproduction by directly interacting with steroid hormones systems. In insects, several classes of phytochemicals, including brassinosteroids and related substances, interfere with molting and reproduction. The effects of the molting-hormone antagonist pesticide DI-31, a brassinosteroid analogue, on Aedes aegypti mosquito larvae were tested in two different exposure scenarios. After static exposure of first-instar larvae, the calculated NOEC, LOEC, and LC(50) values referenced to 19 d were 0.03, 0.036, and 0.04 mg/mL, respectively. Semistatic exposure of fourth-instar larvae revealed them to be slightly less susceptible than the younger larvae (NOEC 0.03 mg/mL, LOEC 0.036 mg/mL, LC(50) 0.049 mg/mL referenced to 19 days). In both cases mortality was immediate and larval development was retarded. This study suggests that A. aegypti could be a useful model for the detection of hormonally active substances such as DI-31.     

Toxicity and removal of heavy metals (cadmium, copper, and zinc) by Lemna gibba

Effects of cadmium, copper, and zinc on the aquatic plant Lemna gibba were determined under controlled conditions; in parallel their removal from the growth medium was followed. The results showed that the three heavy metals affected growth, a physiological stress index defined as the ratio of Chlorophyll to phaeophytin (D665/D665a), and the contents of proline. After 4 days, 10⁻³–10⁻¹ mg/L Cd inhibited growth by 25–100%, reduced D665/D665a by 35–89%, and increased proline content by 44–567%. Under the same conditions, 10⁻⁴–10⁻¹ μg/L Cu inhibited growth by 36–75%, reduced D665/D665a by 19–81%, and increased proline content by 67–288%. Comparable concentrations of Zn had little effect. However, higher concentrations (4, 30, and 50 mg/L) inhibited growth by 50–79%. Also, 0.1 and 30 mg/L induced a small reduction of D665/D665a (−3.8% and −22%) and an increase in proline contents (+144% and +177%). When it was observed, proline accumulation was always transient and the maximum was reached after 4 days. Monitoring metal concentration in the medium showed that L. gibba was able to remove metals from the medium. Zn and Cu removal was biphasic, it was rapid during the first 2 days (> 60% reduction) and slow (10–20%) during the following 8 days. For Cd, removal was linear and depended on the initial concentration. It reached approximately 90% after 6 or 8 days for initial concentrations of 10⁻¹ and 10⁻³ mg/L, respectively.     

Heavy metals in aquatic bryophytes from the Ore mountains (Germany)

Concentration of the metals Ni, Cr, Co, Zn, Mn, Pb, Cd, Cu, Ba, Al, and V as well as the macronutrients Ca, Mg, and K were measured in water and in the aquatic bryophytes Platyhypnidium riparioides, Scapania sp., and Fontinalis antipyretica sampled from streams in the Erzgebirge (Ore Mountains, eastern Germany). These plants, as used to evaluate the spatial distribution of elements in the examined streams, contained elevated levels of all the investigated metals except Sr. The highest levels of Cd (195 mg/kg), Cu (233 mg/kg), Zn (22500 mg/kg), Pb (595 mg/kg), and Co (140 mg/kg) seriously exceed background values. In recent years input of pollutants has decreased in the Erzgebirge area and the deposition can now be addressed as being comparable to that of rural areas without major local or regional influences. This investigation indicates that the studied aquatic mosses reflect part of the pollutant loadings released in the past in the Erzgebirge area of which remnants are still present in the environment. Two models describing the con-centrations of Fe and Zn in aquatic bryophytes in relation to concentrations of some elements in water are presented.     

Agricultural adjuvants: acute mortality and effects on population growth rate of Daphnia pulex after chronic exposure

Acute and chronic toxicity of eight agricultural adjuvants (Bond, Kinetic, Plyac, R-11, Silwet L-77, Sylgard 309, X-77, and WaterMaxx) to Daphnia pulex were evaluated with 48-h acute lethal concentration estimates (LC50) and a 10-d population growth-rate measurement, the instantaneous rate of increase (r1). Based on LC50, the order of toxicity was R-11 > X-77 = Sylgard 309 = Silwet L-77 > Kinetic > Bond > Plyac > WaterMaxx; all LC50 estimates were higher than the expected environmental concentration (EEC) of 0.79 mg/L, indicating that none of these adjuvants should cause high levels of mortality in wild D. pulex populations. Extinction, defined as negative population growth rate, occurred after exposure to 0.9 mg/L R-11, 13 mg/L X-77, 25 mg/L Kinetic, 28 mg/L Silwet, 18 mg/L Sylgard, 450 mg/L Bond, 610 mg/L Plyac, and 1,600 mg/L WaterMaxx. Concentrations that caused extinction were substantially below the acute LC50 for R-11, Kinetic, Plyac, X-77, and Bond. The no-observable-effects concentration (NOEC) and lowest-observable-effects concentration (LOEC) for the number of offspring per surviving female after exposure to R-11 were 0.5 and 0.75 mg/L, respectively. The NOEC and LOEC for population size after exposure to R-11 were (1.25 and 0.5 mg/L, respectively. Both of these values were lower than the EEC, indicating that R-11 does have the potential to cause damage to D. pulex populations after application at recommended field rates. The wide range of concentrations causing extinction makes it difficult to generalize about the potential impacts that agricultural adjuvants might have on aquatic ecosystems. Therefore, additional studies that examine effects on other nontarget organisms and determine residues in aquatic ecosystems may be warranted.     

Phototactic behavior in Daphnia magna Straus as an indicator of toxicants in the aquatic environment

In this study, the phototactic behavior of Daphnia magna was investigated as a possible bioindicator for the following 11 chemicals commonly found in the aquatic environment: benzo(b)fluoranthene, mercury (II) chloride, dimethoate, lindane, linuron, MCPA, TBTO, carbon tetrachloride, thiram, 2,4,6-trichlorophenol and arsenic trioxide. Phototactic response was monitored as the movement of 7 to 8 day-old D. magna individuals. The analysis was carried out using glass test tubes divided radially into two zones, with increasing distance from a light source. For each of the compounds, different concentrations and exposure times were analyzed, and the behavior of the D. magna in each of the treatments compared to the controls in which the chemicals were not added. Using the experimental model described here, all of the 11 chemicals could be detected following exposure times of between 15 min and 48 h. The lowest concentrations detected using this technique were between 2 and 43 times lower than the LC(50) and EC(50) values reported for D. magna. The results of this study show that the analysis of phototactism is a useful method for detecting the presence of a wide range of potentially toxic chemicals found in the aquatic environment.     

Assessing the performance of Hormosira banksii (Turner) Desicaine germination and growth assay using four reference toxicants

This study evaluated the performance of a Hormosira banksii germination inhibition bioassay developed to assess the toxicity of single compounds and complex effluents in the Australasian region. The reproducibility of 48 and 72 h germination and growth toxicity tests was determined using four reference toxicants, namely, ammonia, copper, phenol and zinc. H. banksii spore germination and growth was significantly inhibited following exposure to each of the toxicants. H. banskii spores were most sensitive to ammonia and showed decreasing sensitivity to copper, zinc and phenol. The EC50 values ranged from 0.07 to 0.08 mg L(-1) for ammonia, 0.09 to 0.22 mg L(-1) for copper, 36 to 1068 mg L(-1) for phenol and 19 to 23 mg L(-1) for zinc. Variability of the test method ranged from 14% to 144% and was comparable to that observed for commonly employed bioassays against appropriate reference toxicants.     

Antimicrobial resistance profile of Vibrio species isolated from marine shrimp farming environments (Litopenaeus vannamei) at Ceará, Brazil

Brazilian shrimp culture industry has a great economic importance mainly to the northeast region. However, the accelerated development of this activity has resulted in the emergency of outbreaks of diseases from farming shrimp, and as a consequence the use of antimicrobial drugs to minimize the potential adverse effect under the shrimp production. The inappropriate use of antibiotics in aquaculture is one of the causes for the high incidence of antimicrobial resistant bacteria isolated from aquatic environments that represent a danger for aquatic organisms and human health. There is little information available on the level of antimicrobial resistance in pathogenic bacteria from shrimp farming environment. Therefore, this study aimed to evaluate the phenotypic resistance profile among Vibrio isolates from hatcheries water samples and from cultivated marine shrimp hepatopancreas (L. vannamei). Antimicrobial susceptibility testing was carried out by a standard disc diffusion method and the minimum inhibitory concentration (MIC) of oxytetracycline (OTC) for resistant Vibrio isolates was determinate by broth dilution method. The results showed a high incidence of resistance to ampicillin (45.2%) and to the tetracycline class (38.7%). Florfenicol and nitrofurantoin were 100% effective against Vibrio isolates. In this study, the OTC-resistant Vibrio spp. showed MIC values of more than 400 mg/L and the presence of seawater did not influence the oxytetracycline bioactivity. The occurrence of antimicrobial multiresistance patterns was observed in 29% of Vibrio isolates. Fifty-five percent of multiresistant isolates of Vibrio lost one or more antibiotic resistance phenotype after procedure to curing of resistance plasmids. The oxytetracycline resistance was the phenotype most often lost among plasmid-cured isolates.     

Acute and chronic toxicity of zinc to the mottled sculpin Cottus bairdi

The acute and chronic toxicity of zinc to wild mottled sculpin (Cottus bairdi) was measured with 13-d and 30-d flow-through toxicity tests, respectively. Exposure water hardness was 48.6 mg/L as CaCO3 and 46.3 mg/L as CaCO3 in the acute and chronic tests, respectively; pH was slightly above neutral; and temperature near 12 degrees C. The median lethal concentration (LC50) after 96 h was 156 microg Zn/L, but decreased with exposure duration to a median incipient lethal level (ILL50) of 38 microg Zn/L after 9 d, the lowest zinc LC50 reported for any fish species. The 30-d chronic no-effect and lowest-effect concentrations were 16 microg Zn/L (no mortality) and 27 microg Zn/L (32% mortality), respectively. The ILL50 was 32 microg Zn/L. No sublethal growth differences were observed during the chronic test. Analysis of the results from these tests suggested that mottled sculpin may experience acute and chronic toxicity at zinc concentrations lower than any other fish species tested to date. Protection of aquatic communities in stream reaches contaminated by metals seem to require determination of zinc toxicity to lotic species other than trout and other species amenable to aquaculture.     

Comparative Toxicity of Nine Metals to Two Malaysian Aquatic Dipterian Larvae with Reference to Temperature Variation

A study was conducted to determine the suitability of using selected aquatic dipterian larvae for biomonitoring bioassays. The organisms included a member of the biting midge family that was identified as Culicoides furens and a member of the non-biting midge family, identified as Chironomus plumosus. Median lethal toxicity tests were conducted to observe the variation between metal sensitivities between the two larval forms and how variations in temperature could affect the experimental setup. Nine heavy metals were used in the study. It was observed that the 96 h LC₅₀ (in mg/L) for the different metals was found to be Zn-16.21 (18.55 ± 13.87); Cr-0.96 (1.08 ± 0.84); Ag-4.22 (6.87 ± 1.57); Ni-0.42 (0.59 ± 0.25); Hg-0.42 (0.59 ± 0.25); Pb-16.21 (18.31 ± 14.11); Cu-42.24 (45.18 ± 39.30); Mn-4.22 (7.19 ± 1.25); Cd-0.42 (0.59 ± 0.25) for the Chironomus plumosus and Zn-4.22 (6.56 ± 1.88); Cr-0.42 (0.54 ± 0.30); Ag-0.42 (0.54 ± 0.30); Ni-0.42 (0.54 ± 0.30); Hg-0.04 (0.07 ± 0.01); Pb-0.42 (0.54 ± 0.30); Cu-42.24 (45.18 ± 39.30); Mn-4.22 (6.56 ± 1.88); Cd-0.42 (0.54 ± 0.30) in the case of the Culicoides furens. With temperature as a variable the LC₅₀ values were observed to increase from 2.51 mg/L at 10°C to 4.22 ppm at 30°C and to reduce slightly to 3.72 mg/L at 35°C as seen in the case of Zn. It was also observed that at 40°C thermal toxicity and chemical toxicity overlapped as 100% mortality was observed in the controls. This trend was observed in all metals for both C. plumosus and C. furens. Thus indicating temperature played an important role in determining LC₅₀ values of toxicants.     

Use of the juvenile clam, Mercenaria mercenaria, as a sensitive indicator of aqueous and sediment toxicity

The hard clam is an economically important bivalve and is abundant along the East Coast of the US. The goal of this research was to evaluate the sensitivity of this test species as compared to that of other benthic and epibenthic organisms. Toxic effects of cadmium (inorganic metal), DDT (organochlorine pesticide), and fluoranthene (polycyclic aromatic hydrocarbon) exposure in sediments (10-day) and seawater (24-h) on juvenile (212-350-microm) hard clams Mercenaria mercenaria were determined. The aqueous 24-h LC(50) values were 0.42 mg/L cadmium (95% CL=0.35-0.45 mg/L), 0.61 mg/L DDT (95% CL=0.40-0.95 mg/L), and 0.65 mg/L fluoranthene (95% CL=0.44-1.23 mg/L). Results of sediment toxicity tests indicated that the 10-day LC(50) values were 1.66 mg/kg cadmium (95% CL=1.21-2.28 mg/kg), 5.8 mg/kg DDT (95% CL=4.8-8.3mg/kg), and 1.75 mg/kg fluoranthene (95% CL=1.38-2.09 mg/kg). Based on comparisons to toxicity data for other marine species, these findings suggest that the juvenile clam is one of the more sensitive species to a variety of contaminants and may be a valuable indicator for potential sediment toxicity.     

Nitrite toxicity to crayfish, Astacus leptodactylus, the effects of sublethal nitrite exposure on hemolymph nitrite, total hemocyte counts, and hemolymph glucose

The 48-h acute toxicity range of nitrite to narrow-clawed crayfish, Astacus leptodactylus was within 22 and 70 mg L(-1) (mean 29.43 mg L(-1)). Environmental chloride (100 mg L(-1) chloride) increased the 48-h toxicity of nitrite to a range of 31 and 80 mg L(-1) (mean 49.20 mg L(-1)). Hemolymph nitrite, total hemocyte counts (THCs), and hemolymph glucose were examined in A. leptodactylus exposed to different sublethal nitrite concentrations. The same parameters were also determined for A. leptodactylus exposed to different sublethal nitrite concentrations with additional environmental chloride. Additionally, hemolymph nitrite and THCs were analyzed for crayfish exposed to nitrite-free water after 24 h following a 48-h exposure to nitrite. In the nitrite-exposed tests, hemolymph nitrite increased directly with water nitrite; however, after recovery, nitrite in hemolymph decreased. In the nitrite plus chloride-exposed tests, the accumulation of nitrite in hemolymph was relatively low compared to the nitrite-exposed tests. Thus, hemolymph to environment ratios of nitrite in the nitrite-exposed tests were higher than those of nitrite plus chloride-exposed tests. THCs decreased following nitrite exposure and, in general, increased after recovery. In the nitrite with chloride exposed and recovery from nitrite tests, THCs increased. Hemolymph glucose levels elevated following nitrite exposure, independent of water nitrite concentrations. However, with environmental chloride nitrite exposure did not cause elevation of hemolymph glucose. Hemolymph nitrite accumulation was found to be closely related to the decrease in THCs and increase in hemolymph glucose.     

Toxicity of fluoroquinolone antibiotics to aquatic organisms

Toxicity tests were performed with seven fluoroquinolone antibiotics, ciprofloxacin, lomefloxacin, ofloxacin, levofloxacin, clinafloxacin, enrofloxacin, and flumequine, on five aquatic organisms. Overall toxicity values ranged from 7.9 to 23,000 microg/L. The cyanobacterium Microcystis aeruginosa was the most sensitive organism (5-d growth and reproduction, effective concentrations [EC50s] ranging from 7.9 to 1,960 microg/L and a median of 49 microg/L), followed by duckweed (Lemna minor, 7-d reproduction, EC50 values ranged from 53 to 2,470 microg/L with a median of 106 microg/L) and the green alga Pseudokirchneriella subcapitata (3-d growth and reproduction, EC50 values ranged from 1,100 to 22,700 microg/L with a median 7,400 microg/L). Results from tests with the crustacean Daphnia magna (48-h survival) and fathead minnow (Pimephales promelas, 7-d early life stage survival and growth) showed limited toxicity with no-observed-effect concentrations at or near 10 mg/L. Fish dry weights obtained in the ciprofloxacin, levofloxacin, and ofloxacin treatments (10 mg/L) were significantly higher than in control fish. The hazard of adverse effects occurring to the tested organisms in the environment was quantified by using hazard quotients. An estimated environmental concentration of 1 microg/L was chosen based on measured environmental concentrations previously reported in surface water; at this level, only M. aeruginosa may be at risk in surface water. However, the selective toxicity of these compounds may have implications for aquatic community structure.     

Acute and Sub-Lethal Toxicity of Three POEA Surfactant Formulations to <Emphasis Type="Italic">Daphnia magna</Emphasis>

Polyethoxylated tallowamine (POEA) is a non-ionic surfactant used in many herbicide formulations to increase the ability of active ingredients to penetrate leaf cuticles. However, it has also been shown to disrupt respiratory membranes in aquatic organisms. In this study, Daphnia magna was used to examine the lethal and sub-lethal toxicity of three POEA formulations consisting of 5:1, 10:1, and 15:1 average oxide:tallowamine. The formulation consisting of 10:1 was the most acutely toxic with a 48-h LC50 value of 97.0 μg/L and 15:1 was least toxic at 849.4 μg/L. All formulations inhibited growth at concentrations between 100 and 500 μg/L.