Evaluating ammonia toxicity in sewage effluent to stream macroinvertebrates: I. A multi-level approach

A multi-level approach incorporating instream biological response, water quality, and toxicity testing was used to evaluate the toxicity of ammonia in sewage effluent to macroinvertebrates in two Ozark border streams. Macroinvertebrate community compositions at sites upstream from effluent discharge were most similar, while communities at upstream vs downstream sites were least similar. Upstream sites had abundant mayflies, blackflies, and caddisflies, which were absent immediately below effluent discharge. Water quality was also different at upstream vs downstream sites and was significantly correlated with differences in macroinvertebrate communities (r²=–0.66, P<0.05) when data for all months were combined. However, differences in water quality could not consistently be explained by ammonia, which contributed from <1% to 31% of total variation in water quality among sites.The failure of observed NH₃-N concentrations to consistently explain differences in water quality and macroinvertebrate community composition among sites in field studies was corroborated by results of 96-h, static-renewal, ammonia toxicity tests conducted on Chironomus riparius in undiluted sewage effluent and well water. Ammonia concentrations measured in-stream were not toxic to C. riparius in toxicity tests. By using a multi-level approach, a more realistic evaluation of ammonia toxicity in sewage effluent to macroinvertebrates was obtained than by using methods that focus on only one aspect of effluent toxicity.     

Chronic Toxicity of Ammonia to the Freshwater Bivalve Sphaerium novaezelandiae

The chronic toxicity of total ammonium and unionized ammonia (NH₃) to the native New Zealand freshwater fingernail clam Sphaerium novaezelandiae was assessed in soft water under laboratory conditions. Control survival after 60 days was high (93%) and concentration-response relationships showed the sensitivity of S. novaezelandiae survival was markedly greater to both total and unionized ammonia (6.4× and 4.6×) after 60 days compared with the 30-day exposure at 20°C. Chronic mortality and number moribund (inability to rebury) showed similar sensitivities, but reproduction was a more sensitive endpoint based on a concentration-response analysis. The survival LC50 values for total and unionized ammonia were 3.8 mg (N)/L (pH 7.5) and 0.037 mg (NH₃-N)/L, and reproductive values 0.80 mg (N)/L (pH 7.5) and 0.013 mg (NH₃-N)/L at 60 days. No observed effect concentration (NOEC) values for both survival and reproduction were 0.97 mg (N)/L and 0.011 mg (NH₃-N)/L, and the lowest observed effect concentration (LOEC) values were 5.4 mg (N)/L and 0.046 mg (NH₃-N)/L for survival after 60 days, giving a calculated threshold effect concentration (TEC) of 2.3 mg (N)/L and 0.022 mg (NH₃-N)/L. Comparison of the S. novaezelandiae chronic ammonia sensitivity data with the US EPA criteria showed the survival and reproduction TEC values for total ammonia were 1.9× higher than the chronic criterion, and the lethality value 1.4× above the unionized ammonia criterion. The findings suggest that use of the US EPA criteria would provide minimal protection for S. novaezelandiae for chronic ammonia exposure, and that development of site-specific criteria, covering a wide range of environmental conditions, may be required to adequately protect all life stages of this species. Received: 23 September 1996/Accepted: 27 July 1998     

Comparative Effects of Ammonium and Nitrate Compounds on Pacific Treefrog and African Clawed Frog Embryos

The effects of ammonium nitrate, ammonium chloride, ammonium sulfate, and sodium nitrate on survival and growth of Pacific treefrog (Pseudacris regilla) and African clawed frog (Xenopus laevis) embryos were determined in static-renewal tests. The 10-day LC50s for the three ammonium compounds for P. regilla ranged from 25.0–32.4 mg/L NH₄ -N. The 10-day sodium nitrate LC50 for P. regilla was 578.0 mg/L NO₃-N. LC50s for X. laevis exposed for 4 or 5 days to the three ammonium compounds ranged from 27.5–60.2 mg/L NH₄-N. The sodium nitrate LC50 for X. laevis ranged from 438.4–871.6 mg/L NO₃-N. The lowest LOAEL based on length or weight was 6.1 mg/L NH₄-N for the two species. The lowest LOAELs for NO₃-N were 111.1 mg/L for P. regilla and 56.7 mg/L for X. laevis. Calculated unionized NH₃ comprised 0.5–1.8% of measured NH₄-N concentrations. Potential harm to amphibian populations could occur if NH₄-N and NO₃-N in agricultural runoff or drainage impacts sensitive life stages for a sufficiently long period. Received: 9 April 1998/Accepted: 16 August 1998     

Chronic Toxicity of Ammonia to New Zealand Freshwater Invertebrates: A Mesocosm Study

Freshwater macroinvertebrate communities were established within 12 artificial streams or “toroidal” mesocosms and exposed to three replicated concentrations of ammonia for 29 days at constant temperature (16°C) and pH (median 8.4). The criterion units (CU = measured [ammonia]/US EPA 1985 chronic criterion value) of total ammonia in the LOW, MED, and HIGH treatments were 2.0, 4.8, and 13 CUs respectively, and 1.9, 5.8, and 12 CUs for the unionized ammonia. Macroinvertebrates were tolerant of the ammonia exposures with no significant (p > 0.1) effect on taxa richness; number of taxa in the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT); or the quantitative macroinvertebrate community index (QMCI), a biotic index proposed for assessing effects of organic enrichment in New Zealand streams. Significant differences (p < 0.05) occurred for the mean abundance and the numbers of EPT individuals (QEPT), with the HIGH treatment significantly lower (−41%) than the control for both abundance and QEPT. Of the major species, only the mayflies Deleatidium sp. (Ephemeroptera: Leptophlebiidae) and Coloburiscus humeralis (Ephemeroptera: Oligoneuriidae) showed significant reductions in abundance, with only the caddisflies Beraeoptera roria (Trichoptera: Conoesucidae) and Confluens sp. (Trichoptera: Conoesucidae) showing significant increases in abundance. The abundance of juvenile Deleatidium sp. had a negative concentration-response relationship that resulted in an 82% decrease in abundance in the HIGH treatment. Drift of invertebrates showed no response to ammonia treatments. The 29-day EC₅₀ values for Deleatidium sp. for total and unionized ammonia were 2.15 mg (N)/L (pH 8.4) and 0.145 mg (NH₃-N)/L. No observed effect concentration (NOEC) values were 0.95 mg (N)/L and 0.066 mg (NH₃-N)/L, and the threshold effect concentration (TEC) was 1.49 mg (N)/L and 0.102 mg (NH₃-N)/L. Comparison of the Deleatidium sp. chronic ammonia sensitivity data with the US EPA 1985 chronic criterion value (CCC = 0.45 mg [N]/L, pH 8.4, 16°C) showed the TEC value for total ammonia was 3.3× CCC, and 2.2× higher than the updated US EPA 1998 criteria. The findings suggest that use of the US EPA criteria would provide minimal protection for Deleatidium for chronic ammonia exposure, and that development of site-specific criteria, covering a wide range of environmental conditions, may be required to adequately protect this species. Received: 14 September 1998/Accepted: 24 April 1999     

Toxicity of Un-ionized Ammonia,Nitrite, and Nitrate to Juvenile Bay Scallops, <Emphasis Type="Italic">Argopecten irradians irradians</Emphasis>

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 (LC₅₀) and 95% confidence limits were calculated individually for each. Un-ionized ammonia concentrations above 1.0 mg N-NH₃/L resulted in 100% scallop mortality within 72 h. The 72-h LC₅₀ 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 LC₅₀ 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 LC₅₀ was 4453 mg N/L. Our results indicate that un-ionized ammonia is the most lethal nitrogenous waste component to bay scallops.     

The response of the three broodCeriodaphnia test to fifteen formulations and pure compounds in common use

The three broodCeriodaphnia dubia test was carried out on fifteen formulations and pure compounds presently in general use in a variety of treatment processes or as reference toxicants. The most toxic substances (LC₅₀ (based on survival/EC50 (based on total progeny) <10 mg/L) were metallic Cu, tertiary dodecyl mercaptan, an antioxidant TIA-RCO T-424, Cu(NO₃)₂ · 3H₂O, K₂Cr₂O₇, NALCO 7139-a flocculent, DOWFAX 2EP-a surfactant, TB-66-an algicide and ammonia. Exposure to these compounds elicited the same response fromC. dubia for the two endpoints examined-survival and reproductive success. Two antimicrobials, PROXEL GXL and DOWICIL 75, and the surfactant sodium lauryl sulfate, were slightly toxic (LC₅₀/EC₅₀<100 mg/L) for both endpoints studied. Two coagulants, NALCO 7109 and NALCO 8120 and a flocculent PERCOL 757 were practically nontoxic (LC₅₀>100 mg/L) to slightly toxic (LC₅₀<100 mg/L) when the survival endpoint was examined, but were moderately toxic (EC₅₀<10 mg/L) to slightly toxic (EC₅₀<100 mg/L) when the endpoint of reproductive success was examined. These formulations and pure compounds had generally a declining effect on mean brood size, though there were exceptions to this observation as the broods progressed in number.     

Assessing Caffeine as an Emerging Environmental Concern Using Conventional Approaches

Organic wastewater contaminants, including pharmaceuticals, caffeine, and nicotine, have received increased scrutiny because of their detection in water bodies receiving wastewater discharge. Despite recent measurement in United States streams, caffeine’s effect on freshwater organisms is not well documented. The present study measured caffeine’s lethal and sublethal effects on the freshwater species, Ceriodaphnia dubia, Pimephales promelas, and Chironomus dilutus. These organisms, which are used in standard testing or effluent monitoring, were exposed to aqueous caffeine solutions under static exposure for 48 hours and daily renewed static exposure for 7 days. Averaged responses of 48-hour acute end points indicated that C. dubia was more sensitive to caffeine exposures (LC₅₀ = 60 mg/L) than either P. promelas (LC₅₀ = 100 mg/L) or C. dilutus (LC₅₀ = 1,230 mg/L). Exposure-response slopes confirmed these findings (3% mortality/mg/L for C. dubia; 0.5% mortality/mg/L for P. promelas; and 0.07% mortality/mg/L for C. dilutus). Comparative 7-day responses between C. dubia and P. promelas (LC₅₀ = 46 and 55 mg/L, respectively) were more similar than the broad range of acute values. Sublethal effects measured for caffeine exposure included impaired C. dubia reproduction (IC₅₀ = 44 mg/L) and inhibited P. promelas growth (IC₅₀ = 71 mg/L). According to the results of this study, combined with earlier studies reporting environmental concentrations and product half-lives, caffeine should pose negligible risk for most aquatic vertebrate and invertebrate organisms.     

Reclamation of Wastewater for Polyculture of Freshwater Fish: Bioassays Using Chlorella and Gambusia

The feasibility of using the secondary effluents from two sewage treatment plants in Hong Kong (Yuen Long and Shek Wu Hui) for fish culture was assessed. Total ammonia contents in the two sewage effluents surpassed the level of 2 mg L⁻¹ recommended for wastewater fish culture. The two sewage effluents both needed essential elements for supporting algal Chlorella vulgaris growth, whereas only sewage effluent from Yuen Long had contaminants at toxic levels. Total ammonia in water explained more than 80% variations of toxicity of water samples to Gambusia patruelis, mosquito fish, according to regression analysis. Removal of ammonia from the sewage effluent is necessary before being used for fish culture. In addition, the rather high levels of heavy metals (Cu, Zn, Cd) in the effluent should be closely monitored. Received: 8 October 1999/Accepted: 13 May 2000     

Toxicity of iodine,iodide, and iodate to Daphnia magna and rainbow trout (Oncorhynchus mykiss)

The acute toxicity (96-h LC₅₀) of aqueous stable iodine species (I^–, IO ₃ ^– , I₂) to rainbow trout and Daphnia magna were measured at three individual concentrations of hardness, total organic carbon, and chloride. Rainbow trout were most sensitive to I₂ (LC₅₀0.53 mg/L), and much less sensitive to IO ₃ ^– (LC₅₀220 mg/L) or I^– (LC₅₀860 mg/L). Daphnia magna were equally sensitive to I₂ (LC₅₀0.16 mg/L) and I^– (LC₅₀0.17 mg/L), but were less sensitive to IO ₃ ^– (LC₅₀10.3 mg/L). The external and internal radiological dose imparted by equivalent molar quantities of radioactive ¹²⁵I, ¹²⁹I, and ¹³¹I were calculated for both the Daphnia and trout using the LC₅₀ values obtained from a standard water treatment. As expected, the dose from ¹²⁵I and ¹³¹I would exceed the expected lethal dose rate long before a chemically toxic level is reached. In contrast, a molar concentration of ¹²⁹I likely to cause death by chemical toxicity would impart a radiological dose less than that expected to be lethal. Thus, for short-lived aquatic organisms, risks due to chemical toxicity of ¹²⁹I may exceed risks due to its radioactive emissions.     

Toxicity of underground coal gasification condenser water and selected constituents to aquatic biota

The acute and embryo-larval toxicity of the Laramie Energy Technology Center's Hanna-3 underground coal gasification (UCG) condenser water and its constituents were studied in continuous-flow bioassays. The 96-hr LC₅₀ dilution values for untreated Hanna-3 UCG condenser water were 0.1% for rainbow trout, 0.11% for fathead minnows and the 48-hr LC₅₀ dilution forDaphnia pulicaria was 0.18%. Separate 96-hr acute tests with phenol, ammonia, and ammonia plus phenol showed that these two constituents, acting synergistically, were the major constituents affecting the acute toxicity of this coal conversion effluent to fishDaphnia pulicaria, on the other hand, was relatively insensitive to phenol exposure; the primary constituent of Hanna-3 UCG condenser water affecting this species was ammonia.A previously described model was used for predicting the toxicity of effluents with high concentrations of phenol and ammonia to confirm our hypothesis that the acute toxicity of Hanna-3 UCG condenser water to fish was primarily due to the presence of phenol and ammonia. Using the Hanna-3 concentrations of phenol and ammonia in this formula, it was calculated that the 96-hr LC₅₀ values for rainbow trout and fathead minnows exposed to Hanna-3 condenser water would be 0.11% and 0.28%, respectively; values which are near the observed acute toxicity of Hanna-3 condenser water.In a 30-day embryo-larval exposure, fathead minnow egg hatchability, growth, and survival were significantly reduced at 0.04%, 0.02% and 0.01% Hanna-3 condenser water, respectively. At a Hanna-3 dilution of 0.01%, the phenol and un-ionized ammonia concentrations were calculated to be 0.23 mg/L and 0.14 mg/L, respectively. The phenol and un-ionized ammonia concentrations are within ranges expected to produce the long-term effects which were observed.Work funded under an Interagency Agreement between the U.S. Department of Energy and the U.S. Environmental Protection Agency under Contract No. DE-AS20-79 LC 01761 to the Rocky Mountain Institute of Energy and Environment, University of Wyoming.     

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°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 naphthalene and benzene on fathead minnows and rainbow trout

Fathead minnows (FHM) and rainbow trout (RBT) were used in flow-through bioassays to determine the acute toxicity of benzene and naphthalene, and to determine the embryo-larval effects of naphthalene on FHM. On an acute basis, naphthalene was more toxic than benzene (naphthalene LC₅₀ values were 1.6 mg/L for RBT and 7.9 mg/L for FHM; benzene LC₅₀ values were 5.3 mg/L for RBT and >15.1 mg/L for FHM). In the embryo-larval test naphthalene significantly (= 0.05) reduced FHM growth at concentrations as low as 0.85 mg/L. The highest concentration producing no effect was 0.45 mg/L naphthalene, which was 5.7% of the FHM 96-hr LC₅₀. Based upon long-term no-effects naphthalene concentration, the best estimate of the maximum acceptable toxicant concentration (MATC) was >0.45 to <0.85 mg/L naphthalene.Work funded under an Interagency Agreement between the U.S. Department of Energy and the U.S. Environmental Protection Agency under Contract No. DE-AS20-79 LC 01761 to the Rocky Mountain Institute of Energy and Environment, University of Wyoming     

Toxicity of zinc and bleached kraft mill effluent to larval english sole (Parophrys vetulus) and topsmelt (Atherinops affinis)

Toxicity test protocols were developed for larvae of two species of marine fishes of the Pacific coast of the United States. During winter months, larvae were obtained from adult English sole (Parophrys vetulus) spawned in the laboratory. Newly-hatched, nonfeeding larvae were used in 96-hr experiments to determine their acute sensitivity to inorganic and organic toxicants. Exposure to ZnSO₄ produced a 96-hr LC₅₀ of 14.5 mg Zn/L. A complex and variable organic effluent (untreated bleached kraft mill effluent; BKME) yielded 96-hr LC₅₀s ranging from 1.2–9.3% BKME.Larvae were obtained from eggs collected from wild and laboratory populations of the spring and summer-spawning topsmelt (Atherinops affinis). Both acute (96-hr) mortality and longer-term (7–14 days) growth responses of topsmelt larvae to BKME were determined. Acute toxicity levels (96-hr LC₅₀s) ranged from 6.2–9.7% BKME. No Observed Effect Levels (NOELs) for 7 and 14 day exposures ranged from 1.0–3.0% BKME.     

Effectiveness of Vegetated Drainage Ditches for Domestic Sewage Effluent Mitigation

Plant species have an important role in eco-ditches; however, the Michaelis–Menten kinetic parameters of nutrient uptake, growth rate and purification efficiency of ditch plants and their influences on domestic sewage treatment efficiency are still unclear. Growth rates of all nine species, but especially Lemna gibba, Cladophora and Myriophyllum verticillatum were best in undiluted domestic sewage as opposed to a mixture of domestic sewage. Performance of species to accumulate nutrients was not only species-specific, but was also affected by both sewage treatments. Removal efficiency of nutrients was dependent on both plant species and treatment. Uptake kinetic parameters were significantly affected by both nutrient form and plant species. The maximum uptake rate (Vmax) of NH₄-N was higher than NO₃-N. Similarly, Km values for NH₄-N were greater than NO₃-N. These results could be used to identify plants for sewage treatment efficiency and enhance water quality in eco-ditch treatment systems.     

The Toxicity of Glyphosate and Several Glyphosate Formulations to Four Species of Southwestern Australian Frogs

The acute toxicity of technical-grade glyphosate acid, glyphosate isopropylamine, and three glyphosate formulations was determined for adults of one species and tadpoles of four species of southwestern Australian frogs in 48-h static/renewal tests. The 48-h LC₅₀ values for Roundup? Herbicide (MON 2139) tested against tadpoles of Crinia insignifera, Heleioporus eyrei, Limnodynastes dorsalis, and Litoria moorei ranged between 8.1 and 32.2 mg/L (2.9 and 11.6 mg/L glyphosate acid equivalent [AE]), while the 48-h LC₅₀ values for Roundup? Herbicide tested against adult and newly metamorphosed C. insignifera ranged from 137–144 mg/L (49.4–51.8 mg/L AE). Touchdown? Herbicide (4 LC-E) tested against tadpoles of C. insignifera, H. eyrei, L. dorsalis, and L. moorei was slightly less toxic than Roundup? with 48-h LC₅₀ values ranging between 27.3 and 48.7 mg/L (9.0 and 16.1 mg/L AE). Roundup? Biactive (MON 77920) was practically nontoxic to tadpoles of the same four species producing 48-h LC₅₀ values of 911 mg/L (328 mg/L AE) for L. moorei and >1,000 mg/L (>360mg/L AE) for C. insignifera, H. eyrei, and L. dorsalis. Glyphosate isopropylamine was practically nontoxic, producing no mortality among tadpoles of any of the four species over 48 h, at concentrations between 503 and 684 mg/L (343 and 466 mg/L AE). The toxicity of technical-grade glyphosate acid (48-h LC₅₀, 81.2–121 mg/L) is likely to be due to acid intolerance. Slight differences in species sensitivity were evident, with L. moorei tadpoles showing greater sensitivity than tadpoles of the other four species. Adult and newly emergent metamorphs were less sensitive than tadpoles. Received: 19 February 1998/Accepted: 16 August 1998     

Acute Toxicity of Ammonia,Nitrite and Nitrate to Shrimp <Emphasis Type="Italic">Litopenaeus vannamei</Emphasis> Postlarvae in Low-Salinity Water

Shrimp farming in low salinities waters is an alternative to increasing production, and counteracting disease problems in brackish and marine waters. However, in low-salinity waters, toxicity of nitrogen compounds increases, and there is no available data of its acute toxicity in shrimp postlarvae. This study determined the acute toxicity of ammonia, nitrite and nitrate in Litopenaeus vannamei postlarvae in 1 and 3 g/L salinity, as well as the safety levels. The LC₅₀ confirms that nitrite is more toxic than ammonia and nitrate in low salinity waters, and that its toxicity increases with a decrease in salinity. The safe levels estimated for salinities of 1 and 3 g/L were 0.54 and 0.81 mg/L for total ammonia–N, 0.17 and 0.25 mg/L for NO₂–N, and 5.6 and 21.5 mg/L for NO₃–N, respectively.     

Toxicity of Select Beta Adrenergic Receptor-Blocking Pharmaceuticals (B-Blockers) on Aquatic Organisms

One class of pharmaceutical compounds identified in U.S. and European waters are the B-adrenergic receptor blocking compounds (B-blockers). However, little information is available on the potential aquatic toxicity of these compounds. Therefore, Hyalella azteca, Daphnia magna, Ceriodaphnia dubia, and Oryias latipes (Japanese medaka) were exposed to metoprolol, nadolol, and propranolol to determine potential toxicity. Average 48-h LC₅₀ for propranolol to H. azteca was 29.8 mg/L. The no-observed-effects concentration (NOEC) and lowest-observed-effects concentration (LOEC) for propranolol affecting reproduction of H. azteca were 0.001 and 0.1 mg/L, respectively. The average propranolol and metoprolol 48-h LC₅₀s for D. magna were 1.6 and 63.9 mg/L, respectively. C. dubia 48-h LC₅₀s were 0.85 and 8.8 mg/L for propranolol and metoprolol, respectively. The NOEC and LOEC of propranolol affecting reproduction in C. dubia were 0.125 and 0.25 mg/L, respectively. In O. latipes, the propranolol 48-h LC₅₀ was 24.3 mg/L. Medaka growth was decreased at 0.5 mg/L propranolol. A 2-week medaka reproductive study indicated significant changes in plasma steroid levels; however, no changes in the average number of eggs produced or number of viable eggs which hatched was observed. In a 4-week follow-up propranolol exposure, the total number of eggs produced by medaka and the number of viable eggs that hatched were decreased at concentrations as low as 0.5 μg/L. Based on this study and the expected aqueous environmental exposure levels, adverse effects of propranolol to invertebrate populations is unlikely; however, further reproductive studies are need to elucidate the risk to teleosts. Received: 14 August 2001/Accepted: 4 March 2002     

Toxicity evaluation of ammonium sulphate and urea to three developmental stages of freshwater snails

Studies were performed to evaluate the toxic effects of ammonium sulphate and urea (chemical fertilizers currently applied in ricelands of Cameroon) against eggs, juveniles, and adults of two species of freshwater snails (Helisoma trivolvis andBiomphalaria havanensis). Results obtained from ammonium sulphate tests indicated 24-h LC₅₀ values of 558 mg/L and 669 mg/L for eggs; 393 mg/L and 526 mg/L for juveniles, and 701 mg/L and 657 mg/L for adults ofH. trivolvis andB. havanensis, respectively. Similar analysis with urea revealed LC₅₀ values of 14,241 mg/L and 13,532 mg/L for eggs; 18,255 mg/L and 24,504 mg/L for juveniles and 30,060 mg/L and 26,024 mg/L for adults ofH. trivolvis andB. havanensis, respectively.Following 48 h exposure, the concentrations of ammonium sulphate killing 100% of snails were 1,250 mg/L and 1,000 mg/L for the adults ofH. trivolvis and ofB. havanensis, respectively. Those of urea were computed to be 25,000 mg/L forH. trivolvis and 35,000 mg/L forB. havanensis. In rice culture in Cameroon, these fertilizers are applied at doses of 100 kg/ha (ammonium sulphate) and of 150 kg/ha (urea); hence, the above found concentrations lethal to snails appeared to be 10 to 13 times (ammonium sulphate) and to be 165 to 235 times (urea) higher assuming an average water depth of 10 cm in these ricefields. Therefore, the use of ammonium sulphate and urea as chemical fertilizers in ricelands of the Republic of Cameroon might adversely affect the survival of freshwater snails only in the case of spills or of stressful environmental conditions. Under normal laboratory conditions, both chemicals show a low molluscicidal activity with urea being about 25 to 35 times less potent than ammonium sulphate.     

The influence of season and exercise on the lethal toxicity of cyanide to rainbow trout (Salmo gairdneri)

The lethal toxicity (96-hr LC₅₀) of cyanide (HCN) to juvenile rainbow trout (Salmo gairdneri) varied seasonally and with exercise (swimming at one body length/sec). The trout were acclimated to the 12C test temperature for 3–4 weeks, under a 12 hr photoperiod before being tested at different times of the year. In summer, there was no significant difference of sensitivity between exercised and non-exercised trout. From summer to winter, the 96-hr LC₅₀ for exercised trout remained unchanged at 0.052 mg/L HCN while the LC₅₀ of the non-exercised trout dropped significantly to 0.043 mg/L HCN. The median survival times of the two groups of trout were the same in the summer, but in winter the exercised fish survived twice as long as the non-exercised fish. A longer acclimation period of the non-exercised trout from 4 weeks to 10 weeks during the winter increased resistance to cyanide.     

Bioaccumulation and toxicity of sediment associated herbicides (ioxynil, pendimethalin, and bentazone) in Lumbriculus variegatus (Oligochaeta) and Chironomus riparius (Insecta)

The benthic macroinvertebrates Lumbriculus variegatus and Chironomus riparius were used in toxicity and bioaccumulation tests to determine the toxic concentrations and accumulation potential of sediment associated herbicides. The tested chemicals were ioxynil, bentazone, and pendimethalin. The bioaccumulation tests with L. variegatus were performed in four different sediments, each having different characteristics. Water-only LC₅₀ tests were performed with both L. variegatus and C. riparius. A sublethal effect of model compounds in sediments was assessed by a C. riparius larvae growth-inhibition test. Of the model compounds, ioxynil appeared to be the most toxic, with LC₅₀ values 1.79 and 2.79 mg L⁻¹ for L. variegatus and C. riparius, respectively. The LC₅₀ water concentrations for bentazone were 79.11 and 62.31 mg L⁻¹ for L. variegatus and C. riparius, respectively. Similarly, ioxynil revealed the highest bioaccumulation potential in bioaccumulation tests. The most important characters affecting chemical fate in the sediment seemed to be the organic matter content and the particle size fraction. The sediments with low organic material and coarse particle size consistently showed high bioaccumulation potential and vice versa. In C. riparius growth tests bentazone had a statistically significant effect on larval growth at sediment concentrations of 1160 and 4650 mg kg⁻¹ (P<0.05). It is noteworthy that standard deviations tend to be greater at high chemical concentrations, which addresses the fact that part of the individuals started to suffer. Ioxynil had an effect on the larval growth in other test sediment at the highest concentration (15.46 mg kg⁻¹ dw), in which head capsule length correlated with larval weight, decreasing toward higher exposure concentrations. The current results show the importance of sediment organic matter as a binding site of xenobiotics.