Maximum Acceptable Concentration Research Articles

Regulatory limits for pesticide residues in water (IUPAC Technical Report)

National governments introduced residue limits and guideline levels for pesticide residues in water when policies were implemented to minimize the contamination of ground and surface waters. Initially, the main attention was given to drinking water.Regulatory limits for pesticide residues in waters should have the following characteristics: definition of the type of water, definition of the residue, a suitable analytical method for the residues, and explanation for the basis for each limit.Limits may be derived by applying a safety factor to a no-effect-level, or from levels occurring when good practices are followed and also passing a safety assessment, or from the detection limit of an analytical method, or directly by legislative decision.The basis for limits and guideline values issued by WHO, Australia, the United States, New Zealand, Japan, Canada, European Union, and Taiwan is described, and examples of the limits are provided. Limits have been most commonly developed for drinking water, but values have also been proposed for environmental waters, effluent waters, irrigation waters, and livestock drinking waters. The contamination of ground water is of concern because it may be used as drinking water and act as a source of contamination for surface waters. Most commonly, drinking water standards have been applied to ground water.The same terminology may have different meanings in different systems. For example, guideline value (GV) in WHO means a value calculated from a toxicology parameter, whereas in Australia, a GV is at or about the analytical limit of determination or a maximum level that might occur if good practices are followed. In New Zealand, the GV is the concentration where aesthetic significance is influenced.The Australian health value (HV) is conceptually the same as the WHO GV. The New Zealand maximum acceptable value (MAV) and the Canadian maximum acceptable concentration (MAC) are also conceptually the same as the WHO GV.Each of the possible ways of defining the residues has its merits. A residue limit in water expressed as the sum of parent and toxicologically relevant transformation products makes sense where it is derived from the acceptable daily intake (ADI). For monitoring purposes, where it is best to keep the residue definition as simple as possible for the sake of practical enforcement and economy, theparent or a marker residue is preferable. It is also possible for parent and degradation products (hydrolysis and photolysis products and metabolites) to become physically separated as the water moves through soil strata, which suggests that separate limits should be set for parent and important degradation products.The Commission has made 12 recommendations for regulatory limits for pesticide residues in water. The recommendations will act as a checklist for authorities introducing or revising limits or guidelines for pesticide residues in water.

Increasing the Thermooxidative Stability of Ts–1 Fuel. Decreasing the Acceptable Content of Mercaptan Sulfur

The effect of mercaptan sulfur on the thermooxidative stability (TOS) of TS–1 fuel is analyzed. Recommendations are made on changing the standard for the maximum acceptable concentration of mercaptan sulfur for this fuel in GOST 10227–86 to increase the TOS of the fuel.

Effects of Furrow Irrigation on Corn in the Humid Sub-tropical Mississippi Delta

Corn (Zea mays L.) production in the Mississippi Delta has nearly doubled since 1990 but is more susceptible to aflatoxin and fumonisin contamination when grown under drought. Four corn hybrids -- two Bt and two non-Bt -- were grown at Stoneville, MS under irrigated and non-irrigated treatments in 1999, 2000, and 2001. Furrow irrigation was applied at a rate of 1 inch per application during growth stages R1, R3, and R5 in 1999, R1 in 2000, and R1 and R3 in 2001. Irrigation increased grain yields in 2 out of 3 years. More irrigation treatments in 2000 and 2001 would have likely benefited yields. Yields in 2000 were lower than comparable treatments in 1999 and 2001 due to less weight per kernel indicating drought stress occurred during later reproductive growth (R4 to black-layer). Kernel weights were generally higher in both irrigated and non-irrigated treatments in 2001 than they were in 1999 or 2000. This compensated for having fewer kernels per ear, which likely resulted from drought stress at growth stage V12 in 2001. Differences in test weights were observed among years but not irrigation treatments. The Bt hybrids did not differ from the non-Bt hybrids in yield or mycotoxin levels. Aflatoxin and fumonisin contamination did not differ among years or irrigation treatments. Levels were below maximum acceptable concentrations for both mycotoxins. The hybrid N79-L3 had significantly lower fumonisin levels than the other hybrids.

Biomarkers in toxicology versus ecological risk assessment

Toxicity testing of drugs, pesticides, and hazardous compounds has evolved into a battery of standardized tests conducted in a range of surrogate test organisms. The toxicity of these xenobiotics in terms of their LD 50 and LC 50 (Dose or concentration lethal to 50% of the test population), ED 50 and EC 50 (Dose or concentration producing a specified response in 50% of the test population), MATC (Maximum acceptable toxicant concentration), LOEL (Lowest observable effects level), LOEC (Lowest observable effects concentration), NOEL (No observable effects level) or NOEC (No observable effects concentration) is extrapolated to humans and wildlife. Historical failures in the risk assessment process have been largely due to over reliance on regulatory toxicology and an ‘assembly line’ mentality to toxicology. The importance of toxicokinetics, receptor studies and biomarkers are reviewed, firstly, with reference to toxicological incidences in drug development programmes, and secondly, with reference to improved environmental risk assessment of pesticides and other contaminants. Ecological risk assessments also require multidisciplinary skills to study the entry, distribution, and biological effect and fate of chemicals to fully characterise and understand the potential adverse implications of contamination. Optimum integration of chemical measurements and biomarker responses is a challenge that will lead to an improved understanding of adverse effects and their significance in both human and ecological risk assessment.

PESTICIDE RESIDUES IN THERMAL MINERAL WATER IN GREECE

Eight different hot springs (SPA) in Greece were monitored over a one-year survey for priority pesticide residues. A specific and effective procedure including solid phase extraction in combination with HPLC and GC analytical methods were applied. Samples that were sensitive to nitrogen-phosphorus (NPD) and/or electron capture (ECD) detectors were analysed by capillary gas chromatography. From the twenty-six water samples, pesticide residues were detected in fourteen of them (54%) but no one exceeding the European Union Maximum Acceptable Concentration (MAC). Lindane (γ-BHC) was the most frequently detected pesticide. It was found in nine samples (35%) in concentrations from <0.005 to 0.01 μg/L. Other pesticides detected were phorate (in five samples), propachlor (in two samples) and chlorpyriphos ethyl (in three samples) but in concentrations far below the permissible levels.

Histopathological alterations of white seabass, Lates calcarifer, in acute and subchronic cadmium exposure

Histopathological alterations to white seabass, Lates calcarifer aged 3 months in acute and subchronic cadmium exposure were studied by light and scanning electron microscopy. The 96-h LC 50 values of cadmium to L. calcarifer was found to be 20.12±0.61 mg/l and the maximum acceptable toxicant concentration (MATC) was 7.79 mg/l. Fish were exposed to 10 and 0.8 mg/l of Cd (as CdCl 2H 2O) for 96 h and 90 days, respectively. The study showed that gill lamellae and kidney tubules were the primary target organs for the acute toxic effect of cadmium while in the subchronic exposure, the toxic effect to gills was less than that of kidney and liver. Gill alterations included edema of the epithelial cells with the breakdown of pillar cell system, aneurisms with some ruptures, hypertrophy and hyperplasia of epithelial and chloride cells. The liver showed blood congestion in sinusoids and hydropic swelling of hepatocytes, vacuolation and dark granule accumulation. Lipid droplets and glycogen content were observed in hepatocytes at the second and third month of subchronic exposure. The kidney showed hydropic swelling of tubular cell vacuolation and numerous dark granule accumulation in many tubules. Tubular degeneration and necrosis were seen in some areas.

Experimental investigation on the chemical reduction of nitrate from groundwater

Groundwater is a significant source of water. Adverse health effects have been reported when groundwater with a high nitrate concentration is used for drinking purposes. The objective of this paper was to investigate the effectiveness of a new treatment technology for the reduction of nitrate from groundwater. The optimal operating conditions of chemical nitrate reduction with fine aluminum powder are evaluated through controlled laboratory testing using the standard jar-test apparatus. A maximum of 62% nitrate removal was achieved with the following conditions: 300 mg/l aluminum dose, water temperature of 25°C, pH of 10.7, and initial nitrate concentration of 20 mg/l as N. On completion of the treatment, the concentrations of nitrate, nitrite and ammonia were measured as 8.3, 0.26 and 0.50 mg/l as N, respectively, all within the maximum acceptable concentrations (MAC) of the Canadian guidelines. To ensure adequate quality of the treated water, residue concentrations of total aluminum were also measured for several samples following brief sedimentation, and they averaged 0.07 mg/l. This also complies with the Canadian MAC of 0.1 mg/l. In conclusion, chemical nitrate reduction with aluminum powder is demonstrated to be both effective and safe, and the costs associated with the adaptation of this method may be minimized when combined with conventional water softening processes.

Threshold models for species sensitivity distributions applied to aquatic risk assessment for zinc

Species sensitivity distributions (SSDs) are used in ecological risk assessment to derive maximum acceptable concentrations of toxicants in the environment from a limited set of ecotoxicity data obtained in the laboratory. Such distributions usually employ continuous bell-shaped functions such as the normal and the logistic distribution, which have the disadvantage that an arbitrary cut-off value must be chosen (usually the 5-percentile) to designate the concentration below which the fraction of species exposed above their no-effect level is considered acceptably small. In this paper the possibility is explored of introducing a true no-effect principle in the SSD framework by considering models with a finite lower threshold. Four of these distributions are elaborated, the uniform, triangular, exponential and Weibull distributions. The mathematical representations of these functions were re-parameterized allowing direct estimation of the threshold parameter by nonlinear regression. By way of example, a data set comprising chronic ecotoxicity of zinc to 21 different aquatic organisms was used. The exponential distribution did not describe the data well. The other distributions provided estimates for HC 0 (hazardous concentration for none of the species) between 1.66 and 7.83 μg/l. The triangular distribution fitted best to the data and was consistent with previous models. Since threshold-SSDs incorporate a true no-effect level they may be better communicable as a principle for environmental protection in comparison to the approach based on ‘95% protection’.

Hazard assessment of resmethrin: I. Effects and fate in aquatic systems.

A comparative aquatic hazard assessment of resmethrin was conducted to investigate the need for its restricted use classification by the US. EPA as an adult mosquito control agent. This paper describes the environmental fate and aquatic toxicity of resmethrin. The following paper compares resmethrin to the alternative insecticides. Environmental fate studies indicate that resmethrin has a short photolytic half-life in water (<1 h). Furthermore, it is immobile in soil and biodegradable (half-life = 36.5 d) under aerobic conditions. Laboratory studies with constant 48- to 96-h exposures show it is acutely toxic to fish and invertebrates in the 0.22-15.0 microg/L range. Daphnia magna, pink shrimp (Penaeus duorarum) and rainbow trout (Oncorhynchus mykiss) are the most sensitive and mollusks are the least sensitive species. Chronic laboratory studies indicate that the maximum acceptable toxicant concentrations (MATCs) for resmethrin and D. magna, Pimephales promelas, O. mykiss, and Cyprinodon variegatus are 0.58, 0.52, 0.43, and 10.3 microg/L, respectively. The acute-to-chronic ratios (1.1-7.3) for all species studied indicate that chronic toxicity will not be an issue for resmethrin. Furthermore, the characteristics of acute exposures (48- to 96-h) used in the laboratory will not occur under field conditions because of the short half-life of resmethrin in fresh- and salt-water.

Can early life-stages of the marine fish Sparus aurata be useful for the evaluation of the toxicity of linear alkylbenzene sulphonates homologues (LAS C10-C14) and commercial LAS?

Most commercial household cleaning agents and personal care products contain the anionic surfactant linear alkylbenzene sulphonates (LAS) as the active compound. After their use they are discharged, theoretically after adequate wastewater treatment, into receiving waters finally reaching estuaries and coastal waters. Laboratory toxicity tests are useful tools in determining at which concentration a certain wastewater compound becomes hazardous for an existing group of organisms. Early life-stage toxicity tests include exposure during the most sensitive development period of the organism. In fish, this type of assay has shown to predict accurately maximum acceptable toxicant concentration (MATC) values (comprised in the range defined by the NOEC and LOEC) in fish early life-stage tests. For this reason, larvae of the seabream, Sparus aurata, were exposed to increasing concentrations of LAS homologues (C10-C14) and commercial LAS. Obtained LC50 values ranged between 0.1 and 3.0 mg l and were compared with LC50 values of previous hatching experiments with the same species. Larvae proved to be more sensitive to LAS exposure of individual homologues than eggs, except in the case of commercial LAS. LC50 values can be directly employed to determine their potential risk in a concrete environment with known pollutant concentrations. Dividing the LC50 value with the found homologue concentration and extrapolating with certain security factors proposed by different environmental organisms, potentially hazardous pollutant concentrations may be detected. Average estuarine or coastal LAS concentrations are generally below toxicity limits for this kind of organism, considering that the average alkyl chain length of commercial LAS is 11.6 carbon atoms.

Acute toxicity of tobacco (&lt;i&gt;Nicotiana tobaccum&lt;/i&gt;) leaf dust on &lt;i&gt;Oreochromis niloticus&lt;/i&gt; and haematological changes resulting from sublethal exposure

Experiments were conducted using dry tobacco (Nicotiana tobaccum) leaves aqueous extract to determine the acute toxicity and sub lethal effects on some haematological indices of Oreochromis niloticus using static renewable bioassay method. The extract was found to be toxic with a 48-h LC50 value of 109.6 mg/l. Sub lethal concentrations of the extract were found to have an inverse relationship with the haematological indices assessed. Statistical analysis using ANOVA revealed that there was a significant difference (P < 0.05) in the values of red blood count (RBC) and haemoglobin (Hb). A maximum acceptable toxicant concentration (MATC) of 5 mg/l was found while a safety level of 10.96 mg/l was estimated. Key words: Toxicity, tobacco, haematology, Oreochromis niloticus Journal of Aquatic Sciences Vol.17(1) 2002: 5-8

The sheepshead minnow as an in vivo model for endocrine disruption in marine teleosts: A partial life‐cycle test with 17α‐ethynylestradiol

The sheepshead minnow (Cyprinodon variegatus Lacépède), an estuarine fish species, was exposed to 17alpha-ethynylestradiol (EE2) at nominal test concentrations of 0.2, 2, 20, 200, 400, 800, 1,600, and 3,200 ng/L. Fish were exposed for up to 59 d, from subadult stages to sexual maturity, under flow-through conditions. The exposure period was followed by an evaluation of reproductive success and survival of progeny. The reproductive success of exposed sheepshead minnows, as determined from data on egg production from two subsequent spawning trials, was reduced in fish exposed to 200 ng/L EE2 and, in one spawning trial, in the 20-ng/L treatment. Hatching success was reduced in the progeny of fish exposed to 200 ng/L EE2, but survival was good among fry that successfully hatched. Histological examination indicated generalized edema, damage to gill epithelia, hepatic toxicity, fibrosis of the testis, and evidence of sex reversal, including testes-ova and spermatagonia-like cells in ovaries. The maximum acceptable toxicant concentration (MATC) for gonadal development in males was within the normal range of EE2 concentrations in sewage treatment plant effluents. The exposure regimen and choice of test organism, combined with histological examination, allowed independent evaluation of ecologically significant acute, reproductive and estrogenic endpoints. Estrogen receptor-mediated effects occurred at concentrations where reproductive effects were measurable under standard reproduction assays. The sheepshead minnow appears to be a sensitive in vivo model for partial life-cycle testing of compounds that have the potential to disrupt the endocrine system as well as reproduction in estuarine and coastal marine fish species.

Farm Well Water Quality in Alberta

Abstract On-farm groundwater supplies in Alberta were evaluated for chemical (routine chemistry, trace metals), herbicides and microbiological (total and fecal coliforms) parameters to determine the suitability of domestic drinking water usage based on the Guidelines for Canadian Drinking Water Quality (GCDWQ). The sampling program was conducted between May and October of 1995 and 1996. Thirty-two percent of the 816 farm water wells surveyed (depth range 2 to 284 m) exceeded the GCDWQ for maximum acceptable concentration (MAC) or interim maximum acceptable concentration (IMAC) of at least one parameter. In addition, the water from 92% of the sites exceeded the GCDWQ for at least one of the aesthetic objectives (AO). The chemicals were ranked from most to least frequently exceeding the GCDWQ MAC, in the following order: F &amp;gt;&amp;gt; NO3 −N + NO2−N &amp;gt; As &amp;gt; Se &amp;gt; Pb &amp;gt; B &amp;gt; U &amp;gt; Cr (13, 6, 3, 3, 2, 0.9, 0.4 and 0.2% of all samples, respectively). The parameters ranked from most to least frequently, exceeding the AO, in the following order: TDS &amp;gt; Na &amp;gt; Fe &amp;gt; Mn &amp;gt; pH &amp;gt; SO4 &amp;gt; Cl &amp;gt; Al &amp;gt; Zn &amp;gt; Cu (85, 64, 36, 34, 23, 19, 6, 2, 1 and 0.1 % of the samples, respectively). The majority of the higher concentrations of most inorganic parameters are due to natural geological conditions defined by source aquifer mineralogy. The effects of primary agriculture are likely limited to the 3% herbicide detections and to some nitrate and microbiological contaminations observed; this water should not be used for human consumption without some form of site-specific treatment. Some rural residents may be “mistreating” their water, and a general lack of water testing among rural residents was noted.

Arsenic removal during conventional aluminium-based drinking-water treatment

The changing forms and concentrations of arsenic through aluminium-based coagulation treatment processes were tracked for three drinking-water treatment plants. This has provided direct evidence of where and how arsenic is removed. In general, soluble As(V) is converted to particulate As(V) by adsorption during rapid mixing, and is removed along with naturally occurring particulate arsenic predominantly by clarification. Soluble As(III) tracks through the treatment processes and is converted to soluble As(V) during final chlorination. The ability of a water treatment process to achieve the maximum acceptable concentration for arsenic in drinking water is dependent on the concentration of As(III) in the source water.

Relative Elicitation Potencies of Seven Chemical Allergens in the Guinea Pig Maximization Test.

Dose-response profiles for both induction and elicitation phases were evaluated with seven chemical allergens using the guinea pig maximization test. Considering the risk assessment of contact sensitization in its practical sense, the profile of elicitation would be more critical than that of induction, and it should be evaluated in a maximally induced human population or experimental animals. When mean skin reaction scores in a group of maximally sensitized animals with each allergen were plotted against log challenge concentrations, linear regression lines with good fitness were adapted to all allergens. An elicitation threshold calculated from the linear regression line of each allergen could be used as an index of the relative elicitation potency of a chemical. However, unlike other cases of risk assessment, maximum acceptable concentrations for allergens in consumer products cannot be obtained simply by dividing an elicitation threshold by a fixed safety factor. The value of a safety factor for each allergen should be set on a case by case basis. As a practical matter, consumers are at a risk of exposure to allergens at concentrations greater than elicitation thresholds. Thus a dose-response profile for elicitation in maximally sensitized animals should be included in the evaluation of the risk. We propose to use the area under the linear regression line between the threshold and 1% of the elicitation concentration as a relative elicitation potency index of each allergen, because it reflects the integrated degree of skin reaction that would emerge among a maximally sensitized population exposed to an allergen.

Toxicity of copper sulfate for survival, growth, molting and feeding of juveniles of the tiger shrimp, Penaeus monodon

The aim of this study was to determine the acute and chronic toxicity of copper sulfate for juveniles of Penaeus monodon. The 96-h LC50s (median lethal concentrations) of copper on juvenile P. monodon (0.63±0.13 g) were 3.13 and 7.73 mg/l in seawater of 15‰ and 25‰, respectively. The mortality rates of P. monodon juveniles (0.19±0.02 g) following exposure to 0 (control), 0.45, 0.90, 1.80 and 4.50 mg/l copper after 30 days was 0%, 0%, 5.6%, 22.2% and 55.6%, respectively. After 30 days of exposure, the body weight and total length of shrimps exposed to copper at 0.90 mg/l and higher was significantly lower ( P<0.05) than those in the control. The 30-day EC50 (concentration that reduced weight gain by 50% of that of the controls) and 60-day EC50 were 2.82 and 1.89 mg/l copper, respectively. The ratio of carapace length to total length of shrimps exposed to copper at 0.90 mg/l was significantly higher ( P<0.05) than the controls. Following exposure to copper as low as 0.90 mg/l, P. monodon shortened the time to the first molt, and decreased its growth and molting frequency. Following exposure to copper as low as 5.0 mg/l, P. monodon juveniles (6.25±0.09 g) decreased their feeding. The MATC (maximum acceptable toxicant concentration) was 0.45 mg/l copper based on the growth and molting of shrimps weighing 0.18–1.03 g, and was 1.0 mg/l copper based on the feeding of shrimps weighing 6.25 g.

Sea-nine antifoulant: an environmentally acceptable alternative to organotin antifoulants

This article reviews previously reported data on the performance, environmental fate, and environmental modeling of Sea-Nine™ 211 antifoulant 2 Sea-Nine is a trademark of the Rohm and Haas Company, Philadelphia, PA. 2 (4,5-dichloro-2- n-octyl-4-isothiazolin-3-one). Since organotins are an industry standard, the environmental fate and environmental modeling results of tributyltin (TBT) are compared to those of the Sea-Nine antifoulant for reference. Laboratory and field tests results have shown Sea-Nine antifoulant to be highly effective. Five years of commercial use has confirmed this. Sea-Nine antifoulant and TBT were compared in an environmental risk assessment to predict their effects on the environment. Sea-Nine antifoulant was degraded rapidly in the environment by microorganisms. Its half-life in aerobic and anaerobic microcosm studies was less than 1 h. TBT degraded slowly under aerobic and anaerobic conditions with half-lives ranging from 6 to 9 months. The degradation products of Sea-Nine antifoulant were ring-opened compounds with greatly reduced toxicity. TBT degraded to dibutyltin species, which were still toxic and persistent in the environment. Bioaccumulation studies in fish showed essentially no bioaccumulation of the Sea-Nine biocide. The bioaccumulation of TBT was significant, with bioconcentration factors as high as 10 000. The Sea-Nine antifoulant showed no chronic or reproductive toxicity to marine species, while TBT showed a wide range of effects on growth, development, and reproduction at levels as low as 2 parts per trillion (ppt). Computer modeling using the Exposure Analysis Modeling System (EXAMS) predicted maximum concentrations of Sea-Nine biocide of up to 10 ppt, far below the maximum acceptable environmental concentration (MAEC) of 630 ppt. The maximum predicted concentrations of TBT were as high as 345 ppt, far above the UK Environmental Standard in seawater of 2 ppt.

Physiological Perturbations in Several Generations of Daphnia magna Straus Exposed to Diazinon

Daphnia magna was exposed to sublethal diazinon concentrations (0.05, 0.1, 0.5, 0.75, and 1.0 ng/L) for 21 days. The algae Nannochloris oculata (5×105 cells/mL) was used to feed the daphnids. Chronic toxicity tests were carried out using neonates of F1 (first brood) and F1 (third brood) offspring generations from parentals (F0) preexposed to the organophosphate. The effect of diazinon on survival, reproduction, and growth was monitored for the selected daphnid generations. The parameters used to evaluate pesticide effect on reproduction were mean total young per female, mean brood size, time to first reproduction, mean number broods per female, and intrinsic rate of natural increase (r). Survival and growth (body length) were also determined after 21 days of exposure to the pesticide. Reproduction as well as survival was significantly reduced when diazinon concentration increased in the medium. This effect was greater in F1 (first) and F1 (third) offspring compared to the parental generation (F0) daphnids. The intrinsic rate of natural increase (r) decreased with increasing concentrations of diazinon, especially in those animals from the first and third brood. However, the growth of the exposed organisms decreased in the same order of magnitude in all generations tested. The maximum acceptable toxicant concentration (MATC) was calculated for F0, F1 (first), and F1 (third) generations of D. magna exposed to the pesticide using as parameter of evaluation the intrinsic rate of natural increase (r). The interpolation of these results gave MATC values of 0.62 and 0.07 ng/L pesticide for F0–F1 (first) generations and F1 (third) generation, respectively. Therefore, F1 (third) generation seems to be more sensitive to diazinon than generations F0 and F1 (first). The EC50 values have been derived for some selected parameters on the generations of D. magna exposed to diazinon. EC50 values decreased in F1 (first) and F1 (third) generations compared to the parental generation F0. Expanding the reproduction tests to several generations revealed important information on chronic toxicity that could add to an increased cost-effectiveness in the protection of aquatic environments.

Effects of tetradifon on Daphnia magna during chronic exposure and alterations in the toxicity to generations pre-exposed to the pesticide

Daphnia magna was exposed to some nominal sublethal tetradifon concentrations (0.10, 0.18, 0.22 and 0.44 mg/l) during 21 days. Chronic toxicity tests were carried out using neonates of F 1 first brood (F 1-1st) and F 1 third brood (F 1-3rd) offspring generations from parentals (F 0) pre-exposed to the pesticide. The effect of tetradifon on survival, reproduction and growth was monitored for the selected daphnid generations. The parameters used to evaluate pesticide effect on reproduction were: mean total young per female, mean brood size, time to first reproduction, mean number broods per female and intrinsic rate of natural increase ( r). Survival and growth (body length) were also determined after 21 days of exposure to the pesticide. Reproduction was significantly reduced when tetradifon concentration increased in the medium. This effect was higher in F 1-1st and F 1-3rd offsprings compared to the parental generation (F 0) daphnids. The intrinsic rate of natural increase ( r) decreased with increasing concentrations of tetradifon especially in those animals from F 1-3rd. However, the growth of the exposed organisms decreased in the same order of magnitud in all the generations tested. Survival was not affected after exposure to the selected tetradifon concentrations. The maximum acceptable toxicant concentration (MATC) was calculated for F 0, F 1-1st and F 1-3rd generations exposed to the pesticide using as parameter of evaluation the intrinsic rate of natural increase ( r). The interpolation of these results gave MATC values of 0.13 mg/l pesticide for F 0 and F 1. The EC50 values have been derived for some selected parameters on D. magna exposed to tetradifon. EC50 values decreased in F 1-1st and F 1-3rd generations compared to the parental generation F 0, these results mean that less amount of toxicant would be necessary to reduce the selected parameters to 50% in the first and third broods of D. magna. Expanding the reproduction tests to several broods of a parental generation revealed important information on chronic toxicity that could be used in the protection of aquatic environment.

Structure–activity relationships for acute and chronic toxicity of alcohol ether sulfates

AbstractAcoholethersulfates(AES)areanionicsurfactantscommonlyusedinconsumerproducts. Commercial AES alkyl chain lengths range from C12 to C18, with ethoxylate (EO) units ranging from 1 to 5. Alkyl sulfate is a special case of AES with no EO units. Acute and chronic toxicity tests using Ceriodaphnia dubia via a novel flowthrough method were conducted with 18 AES compounds to derive SARs for effects assessment. In general, acute toxicity (48‐h LC50) increased with increased alkyl carbon chain length and decreased with increased numbers of EO units. Parabolic structure–chronic (7‐d) toxicity relationships were observed for endpoints such as the no‐observed‐effect concentration, lowest‐observed‐effect concentration, maximum acceptable toxicant concentration, EC20, and EC50. A linear relationship of the fractional negative‐charged surface area (FNSA‐3) with acute toxicity was also determined. FNSA‐3 refers primarily to the polar head group of AES and secondarily to the alkyl chain. Seventy percent of the variance in the chronic data was addressed with a quadratic equation relating toxicity to alkyl chain length and EO units. Alternatively, the molecular descriptors FNSA‐3 and S3P (3χp, which is the simple, third‐order path index) were also found to address most of the data nonlinearity. A chronic test conducted with a mixture of four AES components indicated additivity, leading to the support of the performance of an effects assessment of AES as a mixture.