Toxicity Of Un-ionized Ammonia Research Articles

Lethal and Sublethal Toxicity of Un-Ionized Ammonia to Early-Life Stages of Danio rerio.

Un-ionized ammonia (NH3) is a prevalent contaminant found in aquatic ecosystems, frequently associated with complex mixtures of other toxic contaminants. Early embryo-larval stages of zebrafish Danio rerio became an important model for water quality monitoring, and it is necessary to characterize its susceptibility to NH3 exposure. Fertilized eggs were exposed to NH3 concentrations ranging from 0.02 to 5.23 mg NH3 L-1 until 168 h postfertilization (hpf). The lethal concentration to 50% of exposed zebrafish during 96 h was 2.07 mg NH3 L-1, 25% above the median value reported values for early developmental stages of fishes. Sublethal toxicity endpoints indicated the lowest observed effect concentrations for slow blood circulation at 24 hpf, decreased heart ventricular contractions at 72 hpf, incomplete yolk sac absorption at 96 hpf, failure in swim bladder inflation at 96 hpf, developmental retardation at 96 hpf, decreased total length, decreased swimming speed, altered trajectories, and acetylcholinesterase inhibition at 168 hpf of 0.85, 0.06, 0.15, 0.06, 0.15, 0.61, 1.35, 0.35, and 0.85 mg NH3 L-1, respectively. Environmentally relevant NH3 concentrations can affect zebrafish's early development and larval viability, and our results help discriminate NH3 contribution to the toxicity of complex environmental mixtures when zebrafish is used in water quality monitoring.

Behavioral Variables to Assess the Toxicity of Unionized Ammonia in Aquatic Snails: Integrating Movement and Feeding Parameters

Behavioral endpoints are important parameters to assess the effects of toxicants on aquatic animals. These endpoints are useful in ecotoxicology because several toxicants modify the animal behavior, which may cause adverse effects at higher levels of ecological organization. However, for the development of new bioassays and for including the behavior in ecotoxicological risk assessment, the comparison of sensitivity between different behavioral endpoints is necessary. Additionally, some toxicants remain in aquatic environments for a few hours or days, which may lead to animal recovery after toxicant exposure. Our study aimed to assess the effect of unionized ammonia on the movement and feeding behaviors of the aquatic gastropod Potamopyrgus antipodarum (Tateidae, Mollusca) and its recovery after exposure. Four treatments were used: a control and three nominal concentrations of unionized ammonia (0.25, 0.5 and 1 mg N-NH3/L). Each treatment was replicated eight times, with six animals in each replicate. Animals were exposed to unionized ammonia for 48 h (exposure period) and, subsequently, to control water for 144 h (post-exposure period). Two movement variables were monitored without food and five feeding behavioral variables were monitored in the presence of food. Some of the feeding behavioral variables showed higher sensitivity (LOEC = 0.25–0.5 mg N-NH3/L) than the movement behavior variables monitored without food (LOEC = 1 mg N-NH3/L). After exposure to unionized ammonia, animals showed a recovery of most behavioral endpoints. The inclusion of post-exposure period and feeding behaviors in bioassays may make studies more realistic, which is crucial for a proper ecotoxicological risk assessment.

Decreasing toxicity of un-ionized ammonia on the gastropod Bellamya aeruginosa when moving from laboratory to field scale

Along with a steady increasing use of artificial nitrogen fertilizer, concerns have been raised about the effects that high nitrogen loading may have on ecosystems. Due to the toxicity of unionized ammonia (NH3), tolerance criteria have been proposed for ambient water management in many countries; however, these are mainly based on acute or chronic tests carried out under lab conditions run with purified water. Aiming at understanding the responses of organisms to natural exposure to high ammonia concentrations, a Viviparidae gastropod, Bellamya aeruginosa, was tested at three experimental scales: standard 96-h lab test, one-month cage test in 6 experimental ponds with continuous nitrogen inputs, and intensive investigation of the B. aeruginosa from these ponds in spring and winter. The results were: 1) 96-h LC50 in the standard lab test was 0.56 mg NH3-N/L and 343.3 mg TAN/L (total ammonia expressed as N, standardized at pH 7 and 20 ℃). 2) In the one-month cage test, the survival rate was 97% when NH3-N was 0.61 mg/L (i.e., a higher concentration than the lab 96-h LC50) and the body size of the gastropods actually increased with increasing NH3-N concentrations. 3) In the winter-spring investigation, little effect of ammonia on the standing crops of gastropods was found, and the body size of the gastropods tended to increase with increasing ammonia concentrations (NH3-N concentration range of 0.05 ~ 2.06 mg/L). Thus, B. aeruginosa showed higher tolerance to ammonia exposure (NH3-N concentration < 0.81 mg/L) in the field than under laboratory conditions. Our study points to the necessity of considering the relevant scale when determining criteria for ammonia toxicity in water management.

Hemato-biochemical responses and histopathological alterations in the gill and kidney tissues of Osteobrama belangeri (Valenciennes, 1844) exposed to different sub-lethal unionized ammonia

Ammonia is a factor restricting production in aquaculture systems, hindering fish production adversely. A detailed study was planned and conducted using a static water system to scrutinize the toxic effects of unionized ammonia (UIA) on patho-physiological responses of O. belangeri, an important aquaculture candidate for diversification of freshwater aquaculture and endangered species, when exposed to different sub-lethal concentrations of UIA. The 96-h LC50 value of UIA on O. belangeri was found to be 1.36 mg l−1. The sub-lethal toxicity test with three UIA concentrations, i.e., 0.27, 0.68, and 0.80 mg l−1 at different exposure period of 24, 48, 72, and 96-h revealed that exposure to UIA induced a significant reduction in hematological parameters, such as total erythrocyte count (TEC), total leukocyte count (TLC), hemoglobin (Hb), and hematocrit (Hct). Mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) and mean corpuscular hemoglobin concentration (MCHC) also substantially declined due to UIA exposure. Among biochemical parameters, blood glucose, serum glutamate pyruvate transaminase (SGPT), serum glutamate oxaloacetate transaminase (SGOT) and Na+ and K+ ion increased significantly. In contrast, serum protein, alkaline phosphatase (ALP) and serum albumin notably decreased due to ammonia exposure. Fish exposed to different UIA concentrations for 96-h displayed several histopathologic alterations in the gill and kidney tissues. Gill tissues showed several lamellar deformations, while kidney tissues showed significant changes at the level of the glomerulus and tubular epithelium. The NOEL or safe concentration of UIA for this particular fish species was found to be 0.07 mg l−1. The observed patho-physiological alterations in the present study establish the most detail insights of UIA stress in O. belangeri and will enhance the international literature on UIA toxicity.

The evaluation of 3 diets for rearing Hyalella azteca and the influence of diet on acute ammonia toxicity.

Three Hyalella azteca cultures were reared on different diets since birth, reflecting the recommended diets of various investigators. The 3 diets consisted of fish flakes (FF), a mixture of fish flakes supplemented with the diatom Thalassiosira weissflogii (FF-D), and a mixture of fish flakes supplemented with yeast, cereal grass media, and trout chow (FF-YCT). The 3 diets were evaluated by comparing 20 wk of culturing data, along with the organism's response to standard 96-h toxicity testing with ammonium chloride over a range of pH and temperature. Hyalella azteca fed the FF-D diet had the highest overall survival rate (96.6%, standard deviation [SD] 4.3%) compared to those fed the FF diet (92.0%, SD 12.7%), or the FF-YCT diet (91.1%, SD 14.8%), although difference in survival was not statistically significant. Organisms fed the FF-D diet produced a higher number of young per week per adult (6.1, SD 2.8) than the FF diet (5.1, SD 2.2), or the FF-YCT diet (4.0, SD 1.2), although differences were not statistically significant. Of the diets evaluated, H. azteca reared on the FF-D diet were often significantly more resistant to total and un-ionized ammonia toxicity in acute 96-h testing than those reared on the other 2 diets across the 2 temperatures and 5 pHs tested, suggesting this may be the most optimal diet for this species. Environ Toxicol Chem 2016;35:2416-2424. © 2016 SETAC.

Ammonia toxicity to the freshwater planarian Polycelis felina: contrasting effects of continuous versus discontinuous exposures.

Aquatic animals can be exposed to fluctuating concentrations of toxicants. In fact, for some toxicants (i.e., pesticides, ammonia), discontinuous exposure is more environmentally relevant than constant exposure. Responses of aquatic animals to each type of exposure may be different. However, despite the high ecological relevance of behaviour, there is still scarce information on the effects of discontinuous exposure on behaviour. Our study focused on the assessment of unionized ammonia toxicity on the behaviour of a freshwater planarian under continuous exposure (3 days of exposure and 18 days of recovery) versus discontinuous exposure (3 pulses of 1 day with 6 days of recovery between pulses = total 3 days of exposure and 18 days of recovery). Behaviour was assessed as locomotion activity. Bioassays with continuous and discontinuous exposure were performed with one control and five unionized ammonia concentrations (0.14-0.35 mg N-NH3/L). Unionized ammonia in continuous exposure caused less impact on behaviour than equivalent concentrations provided in a discontinuous exposure. By contrast, continuous exposures caused more impact on survival. The discontinuous exposure may allow detoxification during recovery periods, thus increasing the probability of survival in the next pulse. Under continuous exposure, the mortality threshold could be exceeded, and animals could die in greater proportion during exposure as well as the recovery period. We conclude that behavioural activity was a sensitive endpoint to assess the contrasting effects of continuous versus discontinuous exposure and that the response of planarians to discontinuous exposure is different to its response to continuous exposure.

Differences in long-term impacts of un-ionized ammonia on life-history traits of three species ofDaphnia

Daphnia spp. feeds on microalgae and can potentially be used to screen microalgae, which are grown in ammonia-containing wastewater to scavenge available nutrients. A key step for this to work is that Daphnia spp. can still feed in the presence of elevated levels of un-ionized ammonia. To test that, we studied the life-history of three species of Daphnia (Daphnia obtusa, Daphnia similoides, and Daphnia similis) exposed to ammonia-containing water for 21 days. Results showed that survival, development, and fecundity of three tested Daphnia species were negatively affected by un-ionized ammonia. Although there were some differences in details among three species, the three-parameter logistic model fitted the data of three species well and showed similar patterns of response to un-ionized ammonia toxicity. After the 21-day exposure, the increasing NH3N concentrations slightly decreased the survival time by about 1 or 2 days in D. similoides and D. similis, but by 10 days in D. obtusa. The time to maturity was delayed in all three species after being exposed to ammonia. With increasing un-ionized ammonia concentrations, the number of moults decreased from 14.50 to 8.75 in D. obtusa, 13.60 to 11.20 in D. similoides, and 14.25 to 12.25 in D. similis. The overall reproduction per female was reduced by 81.4% in D. obtusa, 82.1% in D. similoides, and 64.6% in D. similis under the NH3N concentration of 0.58 mg/L. The EC50s for total offspring per female in D. obtusa, D. similoides, and D. similis were 0.27, 0.55, and 0.54 mg/L, respectively. Based on the experimental results, D. similoides and D. similis, showing stronger ammonia-resistance than D. obtusa, were more promising for screening microalgae cultivated in ammonia-containing wastewater.

Seasonal variations of the effect of temperature on lethal and sublethal toxicities of ammonia for three common freshwater shredders

In a context of global change, increases in temperature and in ammonia concentration should strongly affect the crustaceans of wetlands. We experimentally examined, at three different seasons (i.e. winter, spring, and summer), the effect of temperature (12, 18, and 24°C) on the lethal (survival rates) and sublethal (oxygen consumption) toxicity of unionized ammonia (NH3) on the amphipods Gammarus pulex and Gammarus roeselii and the isopod Asellus aquaticus. Our results demonstrate (1) a gradient of increasing tolerance and survival from G. roeselii to G. pulex and A. aquaticus, (2) an increasing toxicity of ammonia with temperature, and (3) a strong seasonal variation of the tolerance to ammonia, with a higher tolerance of individuals in winter than in summer. However, the sub-lethal effect of ammonia on the oxygen consumption rate was species dependant and changed according to temperature or season. Global change and resulting variations in crustacean densities will potentially affect the ecosystem functioning (e.g. organic matter recycling).

Analysis of Ammonia Toxicity in Landfill Leachates

Toxicity identification evaluation (TIE) phase I manipulations and toxicity test with D. magna were conducted on leachates from an industrial waste landfill site in Japan. Physicochemical analysis detected heavy metals at concentrations insufficient to account for the observed acute toxicity. The graduated pH and aeration manipulations identified the prominent toxicity of ammonia. Based on joint toxicity with additive effects of unionized ammonia and ammonium ions, the unionized ammonia toxicity (LC50,NH3(aq)) was calculated as 3.3 ppm, and the toxicity of ammonium ions (LC50,NH4+) was calculated as 222 ppm. Then, the contribution of ammonia toxicity in the landfill leachate toxicity was calculated as 58.7 vol% of the total toxicity in the landfill leachate. Other specific toxicants masked by ammonia's toxicity were detected. Contribution rate of the toxicants other than by ammonia was 41.3 vol% of the total toxicity of the landfill leachate.

Acute and chronic un-ionized ammonia toxicity to ‘all-fish’ growth hormone transgenic common carp (Cyprinus carpio L.)

Ammonia is toxic to fish in natural and artificial waters. We evaluated the acute (96 h) and chronic (21 d) toxicity of un-ionized ammonia to GH transgenic common carp (Cyprinus carpio L.) and non-transgenic common carp using a static-renewal bioassay. The 24, 48, 72 and 96 h median lethal concentrations (LC50) of un-ionized ammonia were slightly lower in transgenic carp (2.64, 2.44, 2.28 and 2.16 mg N/L, respectively) than in non-transgenic carp (2.70, 2.64, 2.52 and 2.33 mg N/L, respectively). Similarly, the median lethal time (LT50) was significantly shorter for transgenic carp (1.41, 7.91 and 117.42 h) than for non-transgenic common carp (2.53, 14.06 and 150.44 h) following exposure to 3.86, 3.29, or 2.09 mg N/L, respectively. Moreover, the mortality of transgenic carp was significantly higher than that of non-transgenic carp at all un-ionized ammonia concentrations ((0.91 +/- 0.12), (0.48 +/- 0.06) and (0.12 +/- 0.01) mg N/L) during the 21 d chronic toxicity test. Our results suggest that GH transgenic carp are less tolerant of un-ionized ammonia than non-transgenic carp. Our data are useful for evaluating potential environmental risk, optimizing stocking density in intensive aquaculture and establishing water quality criteria for ammonia in aquaculture.

Tolerance response to ammonia and nitrite in hatchlings paralarvae of Octopus vulgaris and its toxic effects on prey consumption rate and chromatophores activity

Ammonia and nitrite are among the most important water quality parameters. The aim of this study was to determine the acute toxicity of unionized ammonia and nitrite on newly hatched Octopus vulgaris paralarvae. Concretely, survival, feeding and chromatophore activity were examined under different NH3 and NO2− concentrations. The median lethal concentration (LC 50) determined for 24 h was 10.7 ppm for NH3 and 19.9 ppm for NO2−. Based on these results, a concentration range was chosen to test the effect of this environmental contaminants in feeding and chromatophore activity (range between 2.5 and 20 ppm for feeding and 10 and 30 ppm for chromatophore activity), resulting in modifications in both parameters. In fact, a significant decrease (P < 0.05) in Artemia nauplii consumption by the paralarvae was observed with an increase in NH3 and NO2−. Similarly, the chromatophore activity was also affected by concentration of these contaminants, with decreasing response (P < 0.05) when submitted to stressful situations, as the ammonia and nitrite concentration was increased.

Influence of pH, Salinity, Calcium, and Ammonia Source on Acute Ammonia Toxicity to Golden Shiners, Notemigonus crysoleucas

Holding fish at elevated densities with limited water exchange can produce situations where ammonia concentrations are acutely elevated. Ammonia accumulation is considered a major density-limiting factor during transport and holding of golden shiners, Notemigonus crysoleucas, but unionized ammonia (UIA) toxicity to golden shiners has not been studied in detail. Studies were undertaken to examine 48- and 72-h UIA toxicity to golden shiners in response to ammonia source, pH, calcium concentration, and salinity. Shiners were exposed to geometrically increasing increments of UIA under selective environmental conditions, and monitored for mortality within 48 and 72 h. Probit regression was used to calculate median and 1% lethal concentrations of UIA to golden shiners. No difference in toxicity of ammonium chloride salt or aqueous ammonia hydroxide to golden shiners was found. UIA toxicity to golden shiners was much greater than previously reported, and increased as pH increased (72-h LC50: 1.26 mg/L UIA at pH 7; 0.75 mg/L UIA at pH 8; 0.71 mg/L UIA at pH 9). An increase in environmental calcium (75 mg/L) decreased the toxicity of UIA to shiners by 21.7% at pH 8, whereas salinity had no effect on UIA toxicity. To limit golden shiner losses caused by UIA toxicity, calcium chloride should be added to water sources that contain <100 mg/L hardness, and vats and holding tanks should be flushed if UIA concentrations approach 0.13 (pH 7), 0.11 (pH 8), or 0.10 (pH 9) mg/L at 48 h or 0.12 (pH 7), 0.08 (pH 8), or 0.07 (pH 9) mg/L after 72 h.

Tolerance of juvenile pompano Trachinotus marginatus to acute ammonia and nitrite exposure at different salinity levels

The present study was conducted to estimate the acute toxicity of unionized ammonia–nitrogen (NH 3–N) and nitrite–nitrogen (NO 2–N) to juvenile pompano Trachinotus marginatus (0.86 ± 0.21 g) at different salinity levels: 5, 10 (equivalent to its isosmotic point), and 30‰. Fish were acclimated to the different salinities for 10 days and fed ad libitum daily . Groups of five fishes were exposed to five concentrations of NH 3–N and NO 2–N for 96 h plus control groups for each salinity, where no toxicant was added. Test concentrations ranged from 0.28 to 3.53 mg NH 3–N/L and 24.8 to 191.1 mg NO 2–N/L with three replicates per treatment. Tests were run using a standard semi-static system with 100% daily renewal of water and toxicants. The results were based on mortality data registered in different concentrations tested, using the software Trimmed Spearman Karber method. The median lethal concentrations (LC 50) after 96 h of exposure to NH 3–N were 0.66 (0.53–0.81), 1.87 (1.65–2.12) and 1.06 (0.94–1.20) mg NH 3–N/L for 5, 10, and 30‰. The 96 h LC 50 to NO 2–N were 39.94 (36.39–43.84), 116.68 (112.52–121.00) and 37.55 (20.91–67.44) mg NO 2–N/L for 5, 10, and 30‰. Acute toxicity of NH 3–N and NO 2–N to pompano was affected by salinity. Results of the present study show that pompano reared at an isosmotic environment are less sensitive to NH 3–N and NO 2–N. Tolerance to NH 3–N is compromised at reduced salinities, while toxicity of NO 2–N is similar at 5 and 30‰.

Toxicity of Un-ionized Ammonia, Nitrite, and Nitrate to Juvenile Bay Scallops, Argopecten irradians irradians

Juvenile bay scallops (7.2-26.4 mm) were exposed for 72 h to different concentrations of un-ionized ammonia, nitrite, or nitrate. Using the Trimmed Spearman Karber method, 50% lethal concentrations (LC(50)) and 95% confidence limits were calculated individually for each. Un-ionized ammonia concentrations above 1.0 mg N-NH(3)/L resulted in 100% scallop mortality within 72 h. The 72-h LC(50) for un-ionized ammonia was calculated at 0.43 mg N/L. At nitrite concentrations of 800 mg N/L or higher 100% mortality was observed. The 72-h LC(50) for nitrite was calculated at 345 mg N/L. Nitrate was the least toxic, with 100% mortality observed at a concentration of 5000 mg N/L. The calculated nitrate 72-h LC(50) was 4453 mg N/L. Our results indicate that un-ionized ammonia is the most lethal nitrogenous waste component to bay scallops.

Daily variation in short-term static toxicity of unionized ammonia in Litopenaeus vannamei (Boone) postlarvae

Ammonium toxicity of short-duration alkaline events and their variability, as related to 1–30 day-old postlarvae whiteleg shrimp Litopenaeus vannamei (Boone), was assessed by determining medium lethal concentration (LC50) of total ammonium-nitroen (TAN) and NH3-N to 4-h exposures. Exploratory concentrations of TAN were tested at 30°C and pH 9, until mortality from 5% to 95% occurred between 0.9 and 18 mg N L−1. To determine the daily variation of ammonium toxicity, 64 lots of 20 postlarvae were exposed to eight different ammonium concentrations (0, 0.9, 3, 6, 9, 12, 15 and 18 mg N L−1), in two different environmental scenarios: α (pH 8, 26°C) and β (pH 9, 30°C). In environmental scenario α, ammonium concentrations up to 18 mg L−1 pose no short-term mortality risks for ages 1–30 days. In scenario β, mortality was recorded at all ages. The values of LC50 (4 h) for different postlarvae ages have daily variability, ranging from a minimum of 2.54 to a maximum of 6.02 mg L−1 of TAN (0.76 and 1.81 mg N L−1 of NH3-N), for PL3 and PL19, respectively, with a logarithmic linear tendency to increase with age. Postlarvae mortality at 4 h and 3.0 mg N L−1 TAN exposure was lower and less variable in ages greater than 19 days old.

Measurement of Un-ionized Ammonia in Complex Mixtures

The toxicity of un-ionized ammonia, NH3 (aq), in anaerobic digestion of high-nitrogen wastes has been researched extensively. Previous estimates of NH3 (aq) concentration have relied on a simple speciation approach, based only on the acid dissociation constant and the sample pH and total ammonia concentration. The distinction between concentration and chemical activity has generally not been made, despite the potential for resulting errors in the calculation of NH3 (aq) concentration, and the greater applicability of activity to toxicity work. The currently accepted approach for estimating NH3 (aq) concentration is based on assumptions that are not valid in digested animal manure or other concentrated wastes. This work presents an approach for directly measuring NH3 (aq) activity in complex mixtures using gaseous/aqueous equilibrium across microporous tubing. Application of this approach to anaerobic digester samples confirms that the currently accepted approach is not accurate; it overestimated NH3 (aq) activity in unaltered samples by 45-200%. Previous work on the toxicity of ammonia to methanogenesis has probably overestimated the tolerance of consortia to NH3 (aq), due to overestimation of concentrations. The method introduced here is expected to be useful in a range of research on ammonia toxicity and volatilization.

Chronic Toxicity of Un-ionized Ammonia to Early Life-Stages of Endangered Colorado Pikeminnow (Ptychocheilus lucius) and Razorback Sucker (Xyrauchen texanus) Compared to the Surrogate Fathead Minnow (Pimephales promelas)

Ammonia-contaminated groundwater enters the Upper Colorado River from beneath the abandoned Moab Uranium Mill Tailings Pile near Moab, Utah. This reach of the Upper Colorado River was designated as critical habitat for four endangered fish species because it is one of the few existing areas with known spawning and rearing habitats. Un-ionized ammonia (NH3) concentrations frequently exceed 1.00 mg/L in backwaters adjacent to the tailings pile, which exceeds the Utah 30-d average chronic water quality criterion for un-ionized ammonia (0.07 mg/L NH3; temperature 20 degrees C; pH 8.2) by a factor of more than 10. However, there is little published information regarding the sensitivity of endangered fishes to ammonia. We conducted 28-d static renewal studies with post-swim-up larvae to determine the relative sensitivity of Colorado pikeminnow (Ptychocheilus lucius), razorback sucker (Xyrauchen texanus), and the standard surrogate fathead minnow (Pimephales promelas) to NH3. Chronic values (ChVs) for mortality and growth were determined as the geometric mean of the no observed effect concentration and the lowest observed effect concentration based on analysis of variance. The ChVs for growth of fathead minnow, Colorado pikeminnow, and razorback sucker were 0.43, 0.40, and 0.67 mg/L NH3, respectively. The ChVs for mortality of fathead minnow, Colorado pikeminnow, and razorback sucker were 0.43, 0.70, and 0.67 mg/L NH3, respectively. Therefore, the ChVs for mortality and growth were similar for fathead minnow and razorback sucker; however, the ChV for growth was lower than the ChV for mortality for Colorado pikeminnow. Maximum likelihood regression was used to calculate 28-d lethal concentrations (LCx) for each species. The 28-d LC50, LC20, and LC1 values for fathead minnow were 0.69, 0.42, and 0.13 mg/L NH3, respectively. The 28-d LC50, LC20, and LC1 values for Colorado pikeminnow were 0.76, 0.61, and 0.38 mg/L NH3, respectively. The 28-d LC50, LC20, and LC1 values for razorback sucker were 0.54, 0.38, and 0.25 mg/L NH3, respectively. The fathead minnow, Colorado pikeminnow, and razorback sucker are relatively similar in sensitivity and rank at the 35th, 49th, and 31st percentiles, respectively, of the theoretical chronic fish sensitivity distributions for NH3. The existing water quality criteria for NH3, if met by remediation activities at the Moab site, would be protective of these endangered fishes even if fish sensitivity is based on the conservative LC1 value.

Effects of acute and chronic toxicity of unionized ammonia on mud crab, Scylla serrata (Forsskal, 1755) larvae

While the eiects of ammonia on ¢sh and prawn lar- vae are well documented, little is known of its eiect on mud crab (Scylla serrata) (Forsskl, 1755) larvae. Two experiments were conducted in 5 L hemispheri- cal plastic bowls, containing 3 L of ultra-¢ltered and settled seawater and various larval stages of mud crab to (1) determine the acute median lethal concen- tration (LC50) of unionized ammonia and (2) to deter- mine the chronic eiects of unionized ammonia on survival and percentage moulting to zoea and mega- lop stages. The larval stages that exhibited the highest toler- ance to ammonia over 24 h were zoea 1 (LC50 of 4.05 mg L 1 of unionized ammonia) and zoea 5 (LC50 of 6.64 mg L 1 of unionized ammonia). The megalop stage had the lowest total ammonia LC50 at both 24 and 48 h, making it the larval stage most susceptible to total ammonia. Exposure to 6.54 mg L 1 of unionized ammonia resulted in 100% death of all larvae within 24 h. The tolerance of S. serrata larvae to total ammonia did not appear to increase with ontogenetic development. The re- sults indicate that the concentrations at which total ammonia produces an acute or chronic response in mud crab larvae are far higher than those ex- perienced in current larval production systems (0^0.5 mg L 1 of total ammonia) used as industry standards in Australia.

AMMONIA TOXICITY TO JUVENILE ACANTHOBRAMA TELAVIVENSIS (CYPRINIDAE), A CRITICALLY ENDANGERED ENDEMIC FISH IN THE COASTAL PLAIN OF ISRAEL

We assessed the toxicity of ammonia to Acanthobrama telavivensis, a critically endangered endemic cyprinid that until the 1950s was very common in the coastal stream system, but is now restricted to a few unpolluted reaches. Ammonia toxicity was determined by a 96-h LC50 bioassay in a flow-through system with fish mortality as the end point. Acute toxicity of un-ionized ammonia for juvenile A. telavivensis is 1.00 mg l-1 NH3-N (0.94-1.06, 95% confidence limits), which corresponds to 20.1 mg l-1 total ammonia nitrogen at pH 8.0, total hardness of 250 mg/l (as CaCO3), and temperature of 24.2 °C. Acute-to-chronic ratio (ACR) values of 7.2, 10.9, and 16, suggested in the literature, yielded estimated safe ammonia concentrations for A. telavivensis of 0.14, 0.09, and 0.06 mg l-1 NH3-N, respectively, using the accelerated life testing (ALT) procedure. Accordingly, the 0.01% acceptable risk concentrations for 60 and 90 days are 0.17 and 0.16 mg l-1 NH3-N, respectively, agreeing with the safe ammonia concentratio...

Acute toxicity of ammonia (NH3-N) in sewage effluent to Chironomus riparius: II. Using a generalized linear model

Toxicity of un-ionized ammonia (NH3-N) to the midge, Chironomus riparius was compared, using laboratory culture (well) water and sewage effluent (≈0.4 mg/L NH3-N) in two 96-h, static-renewal toxicity experiments. A generalized linear model was used for data analysis. For the first and second experiments, respectively, LC50 values were 9.4 mg/L (Test 1A) and 6.6 mg/L (Test 2A) for ammonia in well water, and 7.8 mg/L (Test 1B) and 4.1 mg/L (Test 2B) for ammonia in sewage effluent. Slopes of dose-response curves for Tests 1A and 2A were equal, but mortality occurred at lower NH3-N concentrations in Test 2A (unequal intercepts). Response of C. riparius to NH3 in effluent was not consistent; dose-response curves for tests 1B and 2B differed in slope and intercept. Nevertheless, C. riparius was more sensitive to ammonia in effluent than in well water in both experiments, indicating a synergistic effect of ammonia in sewage effluent. These results demonstrate the advantages of analyzing the organisms entire range of response, as opposed to generating LC50 values, which represent only one point on the dose-response curve.