Steady-state Bioconcentration Factors Research Articles

Experimental investigation and comparative environmental impact analysis of conventional and naturally occurring kinetic hydrate inhibitors in offshore environments using toxicity and bioconcentration tools

In this present study, an in vivo experiment was carried out to determine the tendencies of a naturally occurring high-phenolic compound red-onion skin extract (HPC-ROSE) and conventional N-Vinylcaprolactam (N-VCAP) kinetic hydrate inhibitors (KHIs) to bio-accumulate in offshore environment through the analysis of their uptake and depuration kinetics by a Fish-Chemical Model using Cyprinus carpio marine invertebrate. This test was performed in the laboratory in a flow through experimental set up according to the guidelines by [49] (Fish-chemical exposure test). The uptake duration was 10 days with a depuration period of twenty days. The inhibitor toxicity test was evaluated by determining the 50 % lethal concentration (LC50) as highlighted by OSPAR Commission protocols. The solubility of the inhibitors was determined by a column elution technique. Similarly, a proton-enabled nuclear magnetic resonance (1HNMR) technique was used to measure the partitioning characteristics of the inhibitors in an immiscible mixture of octanol and water (Kow) by 1HNMR spectroscopy using a benchtop low-field NMR spectrometer. OSPAR Commission and ASTM standard protocols were used for the laboratory investigation of the static sediment toxicity tests. A reference chemical substance of known BCF and solubility (Ethyl Acetate, EtOAc) was used as control to check the experimental progression. The stock solution was prepared by solid phase desorption mechanisms. The HPC-ROSE does not constitute environmentally significant risk to aquatic life owing to its lower BCF values between 215 L/kg - 251.5L/Kg, Log-Kow of 1.2 and higher lethal concentration of 25140 mg/L. Unlike the NVCAP which is very toxic with lower lethal concentration of 1280 mg/L and higher BCF values in the range of 442.5L/Kg to 485 L/kg with Log-Kow of 1.5. Furthermore, Nuclear magnetic resonance (1HNMR) is a simple and reliable method of estimating partition coefficient characteristics (Kow) because the obtained Log-Kow values showed good agreements with that of shake flask and high-performance liquid chromatography techniques. Also, the chemical concentration in water has an inverse relationship with uptake rate constant (K1) and steady-state bioconcentration factor (BCFss). Finally, the theoretically estimated BCFs were higher than the steady-state (BCFss) values that were obtained from laboratory experiments for the different inhibitor samples and at all concentrations. This is due to the route by which Log-Kow was estimated since most of the empirical models are usually one-factor model consisting of partition coefficient and BCF.

Uptake, elimination, and toxicokinetics of selected pharmaceuticals in multiple tissues of Nile tilapia (Oreochromis niloticus) exposed to environmentally relevant concentrations

Pharmaceuticals in aquatic environment displayed adverse effects to fish. The effects are usually related to the internal levels of pharmaceuticals accumulated in specific fish tissues. In this study, we investigated the uptake, elimination, and toxicokinetics of six pharmaceuticals, e.g. naproxen (NAX), diclofenac (DCF), ibuprofen (IBU), carbamazepine (CBZ), fluoxetine (FLX), and sertraline (SER), in 11 fish tissues of Nile tilapia. The experiments were conducted in a flow-through system with an 8-day uptake/8-day elimination periods. The fish exposure groups involved the control, single FLX, and mixture of six pharmaceuticals at environmentally relevant concentration of 4 μg/L. FLX and SER showed the maximum concentrations of 145 and 201 ng/g wet weight, respectively, in fish spleen tissue, while NAX and IBU were not detected in any tissue. The mean concentrations for the pharmaceuticals in Nile tilapia tissues generally followed the order: bile> kidney, gut, stomach, liver> brain, gill, spleen> plasma, skin, muscle. The steady-state bioconcentration factors in various tissues generally range at 0.74–437.58 L/kg. The uptake and elimination toxicokinetics illustrated the rapid accumulation and depuration of pharmaceuticals in fish tissues. The results help to understand the internal bioconcentration, tissue distribution, and toxicokinetics of pharmaceuticals in multiple fish biological compartments.

A Novel Multispecies Toxicokinetic Modeling Approach in Support of Chemical Risk Assessment.

Standardized laboratory tests with a limited number of model species are a key component of chemical risk assessments. These surrogate species cannot represent the entire diversity of native species, but there are practical and ethical objections against testing chemicals in a large variety of species. In previous research, we have developed a multispecies toxicokinetic model to extrapolate chemical bioconcentration across species by combining single-species physiologically based toxicokinetic (PBTK) models. This "top-down" approach was limited, however, by the availability of fully parameterized single-species models. Here, we present a "bottom-up" multispecies PBTK model based on available data from 69 freshwater fishes found in Canada. Monte Carlo-like simulations were performed using statistical distributions of model parameters derived from these data to predict steady-state bioconcentration factors (BCFs) for a set of well-studied chemicals. The distributions of predicted BCFs for 1,4-dichlorobenzene and dichlorodiphenyltrichloroethane largely overlapped those of empirical data, although a tendency existed toward overestimation of measured values. When expressed as means, predicted BCFs for 26 of 34 chemicals (82%) deviated by less than 10-fold from measured data, indicating an accuracy similar to that of previously published single-species models. This new model potentially enables more environmentally relevant predictions of bioconcentration in support of chemical risk assessments.

Uptake, Elimination, and Biotransformation Potential of a Progestagen (Cyproterone Acetate) in Tilapia Exposed at an Environmental Concentration.

Although the distribution of progestagens in aquatic environments has been widely reported, details on their uptake, elimination, and biotransformation in fish have received little attention. This study investigated the uptake, elimination, and biotransformation potential of a progestagen, cyproterone acetate (CPTA), in Nile tilapia ( Oreochromis niloticus) exposed to an environmentally relevant concentration under semistatic regimes. CPTA in tilapia tissues followed a similar pattern, reaching a concentration plateau within 4 days of exposure, and dropping to below limits of quantitation within 4 days of elimination. The calculated steady-state bioconcentration factors suggest a low bioconcentration potential of CPTA in juvenile tilapia. Results of enzymatic hydrolysis treatments revealed that no conjugates of CPTA were present in tissues, but conjugated biotransformation products of CPTA were found in bile, liver, and muscle. Most CPTA entered tissues and then was biotransformed into seven different products by phase I and phase II metabolism. The concentrations of endogenous cortisol were significantly influenced by CPTA in plasma and liver during the uptake period. These findings suggest that biotransformation products of CPTA should be considered for the assessment of the bioconcentration potential and ecological effects of progestagens.

Bioconcentration and Metabolism of Pyriproxyfen in Tadpoles of African Clawed Frogs, Xenopus laevis.

Bioconcentration and metabolism of pyriproxyfen uniformly labeled with 14C at the phenoxyphenyl ring were studied using tadpoles of African clawed frog, Xenopus laevis, exposed to water at the nominal concentrations of 3 and 300 ppb for 22 days under the flow-through conditions, with a following 3 day depuration phase. Neither meaningful mortality nor abnormal behavior was observed in control and exposure groups throughout the study. After the rapid uptake to tadpoles, pyriproxyfen was extensively metabolized and excreted, and as a result, steady-state bioconcentration factors and depuration half-lives ranged from 550 to 610 and from 0.34 to 0.54 days, respectively. The metabolites were mostly distributed in the liver or gastrointestinal tract. The major metabolic reactions were hydroxylation at the 4' position of the phenoxyphenyl group and cleavage of the ether linkage, followed by sulfate conjugation.

Bioconcentration factors and plant–water partition coefficients of munitions compounds in barley

Plants growing in the soils at military ranges and surrounding locations are exposed, and potentially able to uptake, munitions compounds (MCs). The extent to which a compound is transferred from the environment into organisms such as plants, referred to as bioconcentration, is conventionally measured through uptake experiments with field/synthetic soils. Multiple components/phases that vary among different soil types and affect the bioavailability of the MC, however, hinder the ability to separate the effects of soil characteristics from the MC chemical properties on the resulting plant bioconcentration. To circumvent the problem, this work presents a protocol to measure steady state bioconcentration factors (BCFs) for MCs in barley (Hordeum vulgare L.) using inert laboratory sand rather than field/synthetic soils. Three MCs: 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), and 2,4-dinitroanisole (2,4-DNAN), and two munition–like compounds (MLCs): 4-nitroanisole (4-NAN) and 2-methoxy-5-nitropyridine (2-M-5-NPYNE) were evaluated. Approximately constant plant biomass and exposure concentrations were achieved within a one–month period that produced steady state log BCF values: 0.62 ± 0.02, 0.70 ± 0.03, 1.30 ± 0.06, 0.52 ± 0.03, and 0.40 ± 0.05 L kgplant dwt−1 for TNT, 2,4-DNT, 2,4-DNAN, 4-NAN, and 2-M-5-NPYNE, respectively. Furthermore, results suggest that the upper–bounds of the BCFs can be estimated within an order of magnitude by measuring the partitioning of the compounds between barley biomass and water. This highlights the importance of partition equilibrium as a mechanism for the uptake of MCs and MLCs by barley from interstitial water. The results from this work provide chemically meaningful data for prediction models able to estimate the bioconcentration of these contaminants in plants.

Bioaccumulation Behavior of Pharmaceuticals and Personal Care Products in Adult Zebrafish (Danio rerio): Influence of Physical-Chemical Properties and Biotransformation.

The factors influencing bioaccumulation of pharmaceuticals and personal care products (PPCPs) in aquatic organisms are not well understood. The present study involved a comprehensive laboratory investigation to assess the bioaccumulation behavior of several PPCPs in adult zebrafish (Danio rerio). The studied PPCPs included several ionogenic organic compounds (IOCs) such as weak acids and weak bases. Experiments involved two exposure groups (high and low) and a control group, with a 6 day aqueous exposure, followed by a 7 day depuration phase under flow-through conditions. Uptake rate constants (ku) ranged between 0.19 and 8610 L·kg-1·d-1, while depuration rate constants (kd) ranged between 0.14 and 5.14 d-1 in different fish tissues. Steady-state bioconcentration factor (BCFss) values varied widely among the studied PPCPs, ranging from 0.09 to 6,460. In many cases, BCFss values of individual PPCPs differed substantially among different fish tissues. Positive linear relationships were observed between log BCFss values and physical-chemical properties such as octanol-water distribution coefficients (log Dow), membrane-water distribution coefficients (log Dmw), albumin-water distribution coefficients (log DBSAw), and muscle protein-water distribution coefficients (log Dmpw), indicating the importance of lipid-, phospholipid-, and protein-water partitioning. The results also showed that for many PPCPs, the estimated whole-body metabolism rate constant (km) values were comparable to the observed depuration rate (kd), indicating that metabolism plays a major role in the overall elimination of these compounds in zebrafish. An exception was sertraline, which exhibited a kd value (0.4-0.5 d-1) that was much higher than the estimated whole-body km (0.03 d-1). Overall, the results help to better understand the influence of physical-chemical properties and biotransformation on bioaccumulation behavior of these contaminants of concern in aquatic organisms.

Developing earthworm bioconcentration factors of nitrogen-based compounds for predicting environmentally significant parameters for new munition compounds in soil

We investigated the bioconcentration potential of nitrogen-based compounds 4-nitroanisole (4-NAN), 3,5-dinitro-o-toluamide (3,5-DNoTAME), and 2-methoxy-5 nitropyridine (2-M-5-NPYNE) using earthworm Eisenia andrei exposures in aqueous exposure media in sand. Separate toxicity studies were conducted prior to bioconcentration studies using a range of chemical concentrations to establish the sublethal exposure conditions for the earthworms. The objectives of the present studies were to: (1) develop an experimental test system for estimating bioconcentration potentials of new and emerging munition compounds that partition into earthworms, using aqueous exposure media; and (2) apply this experimental model to establish original bioconcentration data for 4-NAN, 3,5-DNoTAME, and 2-M-5-NPYNE. Experimental design includes earthworm exposures to chemicals for up to 14 days in aqueous media (Römbke medium; 0.08mM KCl, 2mM CaCl2, 0.5mM MgSO4, and 0.8mM NaHCO3) in the presence of water-washed coarse sand (0.5–1.0mm) substrate. Concentrations of test chemicals in respective exposure media remained relatively stable during these independent studies. Tissue analyses revealed a rapid uptake of each chemical by the earthworms; a steady state was attained within 24h from commencement of these exposures. Estimated steady-state bioconcentration factors (BCFss; mL/g dry tissue) were 47, 6, and 11 for 4-NAN, 3,5-DNoTAME, and 2-M-5-NPYNE, respectively. These results will contribute to the BCF database being developed for use in models aimed at predicting environmentally significant parameters for new munition compounds in soil.

Tissue distribution and kinetics of dissolved and nanoparticulate silver in Iceland scallop (Chlamys islandica)

The fast expansion of the global nanotechnology market entails a higher environmental and human exposure to nanomaterials. Silver nanoparticles (AgNP) are used for their antibacterial properties; however, their environmental fate is yet poorly understood. Iceland scallops (Chlamys islandica) were exposed for 12 h to three different silver forms, dissolved Ag(I) (Agdiss), small (S-NP, ∅ = 10–20 nm) and large AgNP (L-NP, ∅ = 70–80 nm), labeled with 110mAg, and bioaccumulation kinetics and tissue distribution using in vivo gamma counting and whole-body autoradiography were determined. All Ag forms were readily and rapidly accumulated. Elimination process was also fast and bi-exponential, with mean biological half-life ranging from 1.4 to 4.3 days and from 17 to 50 days for fast and slow compartments, respectively. Most of the radioactivity concentrated in the hepatopancreas. Agdiss and S-NP tissue distributions were similar indicating a rapid dissolution of the latter in the tissues, contrarily to L-NP which appeared to form long lasting aggregates in the digestive system. Estimated steady-state bioconcentration factors (BCF), ranging between 2700 and 3800 ml g−1 for dissolved and particulate silver forms, showed that C. islandica can accumulate significant quantities of Ag in a short time followed by an efficient depuration process.

Bioaccumulation of explosive compounds in the marine mussel, Mytilus galloprovincialis

The bioaccumulative potential of the explosive compounds, 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) were assessed in water only exposures with the Mediterranean mussel ( Mytilus galloprovincialis). Toxicokinetics experiments provided uptake rates, elimination rates, biological half-lives, and bioconcentration factors (BCFs). Kinetic BCFs were 1.61, 0.87, and 0.44, for TNT, RDX, and HMX, respectively, and confirmed the expected low bioaccumulative potential of these weakly hydrophobic compounds based on log K ow. Because apparent steady-state conditions were observed within the 4 h uptake period, steady-state BCFs were also calculated, and were within 20% of kinetic BCFs. TNT was rapidly biotransformed to aminodinitrotoluenes within minutes, while no transformation products were measured for RDX or HMX. Uptake clearance rates varied among the compounds, while elimination rates and associated half-lives were extremely fast (0.15–0.49 h). It is unlikely, based on these data, that exposure conditions for these explosive compounds in the marine environment pose unacceptable risks to mussels, and it appears that potential for trophic transfer is quite low.

Bioaccumulation Kinetics and Bioconcentration Factor of Chlorinated Pesticides in Tissues of Puntius ticto (Ham.)

Bioaccumulation kinetics and bioconcentration factor (BCF) of chlorinated pesticides like Aldrin, Dieldrin, Benzene hexachloride (BHC), and Dichloro-diphenyl-dichloro-ethane (DDT) in fish tissues of Puntius ticto was studied in detail in a continuous fed system. The bioconcentration process is summarized by using a first order uptake model and the steady-state BCF is calculated based on the 30 days exposure. Rate of bioaccumulation of DDT was maximum of 4.6432 µg g−1 wet weight per day in liver tissue whereas it was minimum of 0.0002 µg g−1 wet weight per day in case of Dieldrin in the muscle tissue among the pesticides. It was observed that DDT showed maximum BCF of 89,010 in case of liver tissue of the fish exposed to 30 days. The regression coefficient (r 2) between pesticide concentration and exposure time varied between 0.6212 and 0.9817 indicating high correlation. Based on actual calculated BCF values, the octanol–water partition coefficient (K ow) values were predicted. In order to prove the hydrophobic property of chlorinated compounds and its affinity towards lipid, the K ow is predicted. Results showed that pesticide burden differ from tissue to tissue and can be correlated to the lipid content, size, exposure time, and species.

Comparing Polychlorinated Biphenyl Concentrations and Patterns in the Saginaw River Using Sediment, Caged Fish, and Semipermeable Membrane Devices

Three techniques of assessing bioavailable polychlorinated biphenyls (PCBs) in the Saginaw River, MI, were compared: sediments, caged fish, and semipermeable membrane devices (SPMDs). SPMDs and caged fish were placed in the river for 28 days at five sites where sediments were also sampled. The samples were analyzed for PCB congeners to determine concentrations and patterns. Total PCB concentrations ranged from 33 to 280 ng/g (dry weight) in sediments, 46 to 290 ng/g (wet weight) in caged fish, and 77 to 790 ng/g in SPMDs. Previously reported rates of PCB accumulation by SPMDs were used to estimate aqueous concentrations from the PCB concentrations detected in the SPMDs. Sediment-water partition coefficients were used to estimate aqueous PCB concentra tions from sediment. Steady-state bioconcentration factors and depuration rate constants were used to estimate dissolved PCB concentrations from caged channel catfish. Relative PCB patterns from the SPMDs, caged fish, and sediment were compared using principal components analysis. SPMD and sediment samples provide complementary information. Sediments reflect long-term accumula tion and weathering, while SPMDs integrate water concentrations only during the sampling period. Because of higher water solubilities of lower-chlorinated PCBs these predominate in the SPMDs as compared to in the fish and sediments. Contaminant profile differences between caged fish and SPMDs are likely due to metabolism and depuration of certain PCB congeners by fish.

Bioconcentration and Metabolism of Thiabendazole [2-(4-Thiazolyl)-1H-benzimidazole] in Bluegill Sunfish, Lepomis macrochirus

The steady-state bioconcentration of thiabendazole (TBZ) in the bluegill sunfish was determined in a dynamic (flow-through) bioconcentration test. Fish were exposed to 2.24 ppb of 14 C-labeled TBZ. The TBZ concentration was monitored in both the fish and water during a 28-day uptake period and the subsequent 14-day depuration period. Uptake rate constants (k 1 ), depuration rate constants (k 2 ), and steady-state bioconcentration factors (BCF, k 1 /k 2 ) were calculated for whole fish, viscera, and edible tissues. The resulting BCF values were 96.5 (whole fish), 637.6 (viscera), and 23.0 (edible portion). Clearances of TBZ residue of >95% for the whole fish and >98% for the viscera occurred by the end of the depuration period. Homogenates of edible and visceral tissues were incubated with Glusulase; the ethyl acetate extracts of the incubates were purified and analyzed by HPLC for TBZ and 5-hydroxy-TBZ (5-HO-TBZ), the major mammalian metabolite of TBZ. Of the radioactivity isolated from the edible tissues, 59% was associated, on the basis of its HPLC behavior, with TBZ; smaller portions (32 and 7%, respectively) were associated with 5-HO-TBZ and an unidentified TBZ-related compound. With respect to the radioactivity isolated from the visceral tissues following sequential use of Glusulase and acid hydrolysis, approximately half was associated with 5-HO-TBZ and ∼8% with TBZ. Low-level peaks of radioactivity were observed at five other retention times; these unidentified species accounted for about 28% of the radioactivity isolated from the visceral tissues, with none accounting for more than 10% of the isolated radioactivity.

Bioaccumulation Potential of 4‘‘-epi-(Methylamino)-4‘‘-deoxyavermectin B1a Benzoate (Emamectin Benzoate) in Bluegill Sunfish

Rapid uptake of [5-3H]MAB1a by bluegill was observed under flow-through aqueous conditions, attaining steady-state concentration by about 21 and 10 days, respectively, in whole fish and viscera. Uptake by fillet was, by comparison, much lower, and steady state was not attained by 28 days. Residue levels on the final exposure day (i.e., day 28) were 90, 40, and 128 μg/kg, respectively, in whole fish, fillet, and viscera. Following 14 days of depuration, these residue levels all declined by about 90%. The steady-state bioconcentration factors for whole fish, fillet, and viscera were 80, 30, and 116, respectively, indicating that emamectin benzoate will neither bioconcentrate in individual aquatic organisms nor biomagnify in the food chain. Analysis of 28-day-exposed fish by HPLC showed that the only significant metabolite was the N-demethylated derivative, comprising about 14% and 9%, respectively, of total residues in fillet and viscera, while parent emamectin benzoate was about 63% and 49%, respectively. ...

3H]‐2,3,7,8‐TCDD uptake and elimination kinetics of medaka (Oryzias latipes)

AbstractUptake and elimination rate constants for [3H]‐2,3,7,8‐tetrachlorodibenzo‐p‐dioxin ([3H]TCDD) were estimated by exposing medaka (Oryzias latipes) to [3H]TCDD in flowing water with no solvent carriers. Uptake was determined from body burdens measured on exposure days 0, 2, 4, 6, 10, and 12. Elimination was quantified from whole fish after 28, 90, and 175 d in uncontaminated water. Medaka accumulated [3H]TCDD at a rapid rate, achieving residues 24,000 times the water concentration after 12 d, with no indication of approach to steady state. After 6 months in uncontaminated water, the pg TCDD/g decreased by 69%, much of the decrease due to growth dilution as evidenced by only a 47% decrease in the pg TCDD/fish. Uptake and elimination rate constants (2,300 ml/g/d and 0.0045/d, respectively) were estimated by fitting a one‐compartment, linear, mass‐balance model to the data, adjusting for growth rate. The experimental design, including solvent‐free delivery of [3H]TCDD, exposure at concentrations below maximum water solubility, and measurement of fish growth and lipid content during a 6‐month elimination phase, resulted in a predicted steady‐state bioconcentration factor (BCF) for medaka of 510,000, a number considerably higher than previously reported for dioxin BCFs. Kinetic parameters were used to successfully predict TCDD BCF in medaka exposed independently.

A field study of cadmium dynamics in periphyton and in Hyalella azteca (crustacea: amphipoda)

We studied the dynamics of Cd uptake and depuration in epilithic periphyton and in the grazing amphipod Hyalella azteca. Both stable Cd, sufficient to achieve an aqueous concentration of 90 ng L−1, and its radiotracer 109Cd, were added during 1987 to the epilimnion of oligotrophic Lake 382 of the Experimental Lakes Area in northwestern Ontario. Cadmium dynamics within both periphyton and Hyalella were rapid, with equilibrium being approached within two weeks. For periphyton, the Cd uptake rate constant (Kuw) was 3.8×104 d−1 with a depuration rate of 0.29 d−1. For Hyalella the depuration rate was 0.36 d−1, 10% due to growth dilution and 90% to excretion or desorption. The total Cd uptake rate (kut) by Hyalella was 6.1×104 d−1, with more of the uptake (58%) derived from food (periphyton) than from water. Hyalella assimilated 80% of ingested Cd. Steady-state bioconcentration factors (BCF) were at least 10-fold higher than previously published values for Amphipoda. In periphyton and Hyalella the BCF were 1.2×105 and 3.2×105, respectively.

Environmental effects of the usage of avermectins in livestock

Abamectin (avermectin B 1) and ivermectin (22,23-dihydroavermectin B 1) are high molecular weight hydrophobic compounds, active against a variety of animal parasites and insects. Numerous environmental fate and effects studies have been carried out in the development of these two compounds as antiparasitic agents and for abamectin as a crop protection chemical. They were found to be immobile in soil ( K oc≥4000), rapidly photodegraded in water (degradation half-life ( t 1 2 ) in the summer 0.5 days or less) and as thin films on surfaces ( t 1 2 <1 day ), and aerobically degraded in soil (ivermectin in soil/feces mixtures ( t 1 2 ) = 7–14 days ; avermectin B 1a in soils, ( t 1 2 =2–8 weeks ) to less bioactive compounds. Abamectin is not taken up from the soil by plans, nor is it bioconcentrated by fish (calculated steady-state bioconcentration factor of 52, with rapid depuration). Daphnia magna is the fresh water species found to be most sensitive to ivermectin and abamectin (LC 50 values of 0.025 and 0.34 ppb respectively); fish (e.g. rainbow trout) are much less sensitive to these compounds (LC 50 values of 3.0 ppb and 3.2 ppb, respectively). In the presence of sediment, toxicity toward Daphnia is significantly reduced. The metabolism and degradation of ivermectin and abamectin result in reduced toxicity to Daphnia. Abamectin and ivemectin possess no significant antibacterial and antifungal activity. They display little toxicity to earthworms (LC 50 values of 315 ppm and 28 ppm in soil for ivermectin and abamectin, respectively) or avians (abamectin dietary LC 50 values for bobwhite quail and mallard duck of 3102 ppm and 383 ppm, respectively), and no phytotoxicity. Residues of the avermectins in feces of livestock affect some dung-associated insects, especially their larval forms. This does not delay degradation of naturally formed cattle pats under field conditions; however, in some cases, delays have been observed with artificially formed pats. Based on usage patterns, the availability of residue-free dung and insect mobility, overall effects on dung-associated insects will be limited. As abamectin and ivermectin undergo rapid degradation in light and soil, and bind tightly to soil and sediment, they will not accumulate and will not undergo translocation in the environment, minimizing any environmental impact on non-target organisms resulting from their use.

On the role of blood proteins for uptake, distribution, and clearance of waterborne lipophilic xenobiotics by fish: A linear system analysis

Pharmacokinetic and toxicokinetic system parameters in fish, like gill uptake and elimination efficiencies and mean body residence times of waterborne nonmetabolizing organic xenobiotics, are defined within the framework of linear input-output response theory. Quantitative estimates of these parameters derive from combining (i) a refined flow-limited approach of the countercurrent gill model with (ii) available correlation data of the steady state bioconcentration factor (BCF s) as well as (iii) the blood/water partition coefficient (β) with the octanol/water partition coefficient (K ow) of the chemical compound. Predictions from the model are compared to empirical results on short and long term exposure experiments with the rainbow trout ( Oncorhynchus mykiss).

Predicting Bioaccumulation of Chlorinated Dioxins and Furans in Fish Near Canadian Bleached Kraft Mills

Abstract The use of bioaccumulation factors (BAFs), biota/sediment accumulation factor (BSAF) and a simplified kinetics-based food chain model, for the prediction of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,ß-tetrachlorodibenzofuran (TCDF) levels in biota near chlorine bleached kraft pulp mills was investigated. Data from recent (1988-90) Canadian fish, sediment and effluent monitoring studies were utilized. BAFs for TCDD in suckers (Catostomus sp.) and whitefish ranged 1.8 × 106 to 4.2 × 106 and those for TCDF from 1.0 × 106 to 3.0 × 106. These “field-derived” BAFs , which were calculated from levels in whole fish or muscle and estimated river water concentrations, exceeded laboratory-derived steady-state bioconcentration factors by 10 to 100-fold. BSAF’s for TCDD and TCDF in suckers from 17 riverine sites averaged 0.47 and 1.44, respectively. Weak but statistically significant correlations were found between log10 TCDD and TCDF concentrations in suckers and whitefish lipid and log sediment organic carbon. A wide range of BSAFs were found for crayfish, mussels and benthic insect larvae exposed to particle-bound TCDF in an experimental lake mesocosm indicating that use of BSAF as a predictive tool requires site specific information such as food chain length and habitat type. A food chain model, based on the work of Thomann and Connolly, predicted TCDD and TCDF concentrations in whitefish and suckers at most locations, despite many simplifying assumptions. The greatest simplification was the use of a mean annual flow and simple dilution of mill effluent to estimate dissolved and particle-associated TCDD/TCDF concentrations. Use of bed sediment concentrations to predict concentrations in upper trophic levels did not improve model predictions. With emissions of TCDD and TCDF declining, further application of food chain models will require detailed knowledge of the fate of contaminants in bed and suspended sediments and river hydrodynamics.

Uptake and elimination of lindane by Lymnaea palustris (mollusca: Gastropoda): A pharmacokinetic approach

The uptake and elimination of lindane by adult Lymnaea palustris (Müller) were studied using a static contamination system. First-order one-and two-compartment models were used to quantitatively describe these phenomena. The accumulation of residues was triphasic and the observed steady-state bioconcentration factor lay between 36.8 and 56.4 but did not significantly depend on the initial lindane concentration (6, 60, and 600 μg liter −1). Accumulation was inferior to that observed for other aquatic organisms and this was attributed to the relatively low lipid content of L. palustris tissues (mean of 0.81 ± 0.17% of fresh weight). The transfer of snails to lindane-free water after 72 hr of exposure was followed by a biphasic elimination of residues with a halflife of 0.7 hr in the central compartment and of 130.2 hr in the peripheral compartment. Additional experiments showed that the residues enter the snails through the foot and are afterward stocked within the visceral mass which contains approximately three times more lipids than the foot (1.03 ± 0.13% of fresh weight vs 0.37 ± 0.03%).