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Archives of Environmental Contamination and Toxicology (v.50, #1)
Pesticide and Pathogen Contamination of Vegetables in Ghana’s Urban Markets by P. Amoah; P. Drechsel; R. C. Abaidoo; W. J. Ntow (pp. 1-6).
The objective of the study was to determine and compare the current level of exposure of the Ghanaian urban population to hazardous pesticide and fecal coliform contamination through the consumption of fresh vegetables produced in intensive urban and periurban smallholder agriculture with informal wastewater irrigation. A total of 180 vegetable samples (lettuce, cabbage, and spring onion) were randomly collected under normal purchase conditions from 9 major markets and 12 specialized selling points in 3 major Ghanaian cities: Accra, Kumasi and Tamale. The samples were analyzed for pesticide residue on lettuce leaves, total and fecal coliforms, and helminth egg counts on all three vegetables. Chlopyrifos (Dursban) was detected on 78% of the lettuce, lindane (Gamalin 20) on 31%, endosulfan (Thiodan) on 36%, lambda-cyhalothrin (Karate) on 11%, and dichloro-diphenyl-trichloroethane on 33%. Most of the residues recorded exceeded the maximum residue limit for consumption. Vegetables from all 3 cities were fecally contaminated and carried fecal coliform populations with geometric mean values ranging from 4.0 × 103 to 9.3 × 108 g–1 wet weight and exceeded recommended standards. Lettuce, cabbage, and spring onion also carried an average of 1.1, 0.4, and 2.7 helminth eggs g–1, respectively. The eggs were identified as those of Ascaris lumbricoides, Ancylostoma duodenale, Schistosoma heamatobium, and Trichuris trichiura. Because many vegetables are consumed fresh or only slightly cooked, the study shows that intensive vegetable production, common in Ghana and its neighboring countries, threatens public health from the microbiologic and pesticide dimensions. Standard recommendations to address this situation (better legislations, law enforcement, or integrated pest management) often do not match the capabilities of farmers and authorities. The most appropriate entry point for risk decrease that also addresses postharvest contamination is washing vegetables before food preparation at the household or “chop” bar (street restaurant).
Joint Toxicity of Cadmium and Phenanthrene in the Freshwater Amphipod Hyalella azteca by K. A. Gust (pp. 7-13).
The joint toxicity of combined metals and polynuclear aromatic hydrocarbons is poorly understood and may deviate from the summed concentration responses of the individual pollutants. The freshwater amphipod Hyalella az-teca was exposed to sediment-amended Cd and phenanthrene (Phen) individually and in combination using United States Environmental Protection Agency 10-day sediment toxicity bioassays with lethality and growth end points. The lethal joint toxicity of Cd and Phen was investigated separately in 24-, 48-, and 72-hour aqueous exposures. In sediment exposures, a sublethal concentration of Phen (144 mg kg−1) in combination with Cd increased mortality across a range of Cd concentrations and decreased the 10-day LC50 for Cd from 523 mg kg−1 (461 to 588, 95% confidence interval [CI]) to 263 mg kg−1 (214 to 312, 95% CI). In contrast, sublethal concentrations of Phen had no effect on the lethal toxicity of Cd in aqueous exposures. Combined sediment-amended Cd and Phen acted independently on growth rate. Rate decreases were driven primarily by Cd. Our findings indicated that association with sediment influences the joint toxicity of Cd and Phen. Thus, mixtures of Cd and Phen may cause synergistic or independent toxicity in H. azteca depending on the end point investigated and the experimental protocol employed. As an implication of these results, the interpretation of standardized toxicity bioassays, including whole-effluent toxicity tests and single-compound toxicity tests, must be made with caution. These assessment protocols may underestimate potentially hazardous mixture effects in sediment environments. Therefore, risk assessment protocols for environments containing metal–PAH mixtures must include robust methods that can detect possible interactive effects among contaminants to optimize environmental protection.
Induction of CYP1A mRNA in Carp (Cyprinus carpio) from the Kalamazoo River Polychlorinated Biphenyl-Contaminated Superfund Site and in a Laboratory Study by M. A. Fisher; C. Mehne; J. C. Means; C. F. Ide (pp. 14-22).
The Kalamazoo River Superfund site in Michigan is contaminated with polychlorinated biphenyls (PCBs), which were heavily discharged into the river from several paper companies as part of the deinking process in the 1950s through 1970s. We characterized biomarkers of chronic PCB exposure in a resident fish population using real-time reverse transcriptase–polymerase chain reaction to examine mRNA expression levels of multiple genes in carp (Cyprinus carpio) liver from PCB contaminated and reference sites in the Kalamazoo River. We also measured these same genes in juvenile carp exposed to dietary PCBs for 4 months. Kalamazoo River carp had significantly increased levels of cytochrome P450 1A (CYP1A) mRNA as did carp fed PCBs in the laboratory. No significant mRNA upregulation occurred in the specific oxidative stress genes (gamma-glutamylcysteine synthetase and magnesium superoxide dismutase) and metabolic genes (phosphoenolpyruvate carboxykinase and nucleolin) examined. These data are consistent with the idea that carp from the Kalamazoo River Superfund Site are responding to PCB exposure via upregulation of CYP1A independent of activation of the oxidative stress response genes normally thought to be co-regulated with CYP1A.
Time-Course Variations of DNA Damage and Biomarkers of Oxidative Stress in Tilapia (Oreochromis niloticus) Exposed to Effluents From a Swine Industry by P. L. Lima; J. C. Benassi; R. C. Pedrosa; J. Dal Magro; T. B. Oliveira; D. Wilhelm Filho (pp. 23-30).
DNA damage (Comet assay), lipoperoxidation levels (TBARS), and several biomarkers of oxidative stress such as catalase (CAT), glutathione reductase (GR), glutathione peroxidase (GPx), glutathione S-transferase (GST), and contents of reduced (GSH) and total (TG) glutathione were measured in liver and blood (Comet assay) of tilapia (Oreochromis niloticus) exposed for 7, 15, 30 (subchronic exposure), 60, and 90 days (chronic exposure) to two treatment lagoons of a swine-processing plant, the first an anaerobic lagoon and the second a final treatment lagoon. After the 15th day, TBARS increased in fish exposed to both lagoons, decreased on the 30th day, and on the 90th day remained similar to controls. Fish exposed subchronically and chronically to both effluents showed consistently greater DNA damage. The CAT and GPx activities showed similar profiles and were induced only during the first week and during the first and second months. GST activity was induced throughout the experimental period. On the other hand, GR activities showed inverted profiles, with progressively decreased activities in the liver of fish exposed to the anaerobic lagoon, and progressively increased activities in fish exposed to the final lagoon. GSH showed higher contents in liver after 60 and 90 days of exposure to the final lagoon. GSSG contents were higher in fish exposed to the final lagoon throughout the experimental period. After 15 days, tilapia exposed to both lagoons showed enhanced total glutathione contents. The hepatic antioxidant system and biomarkers of oxidative stress such as DNA fragmentation and TBARS contents of tilapia exposed to both lagoons presented biphasic profiles. These changes in the antioxidant status also indicate that the industrial treatment is not adequate to avoid damaging environmental effects.
Distribution of Pesticide Residues Within Homes in Central New York State by S. K. Obendorf; A. T. Lemley; A. Hedge; A. A. Kline; K. Tan; T. Dokuchayeva (pp. 31-44).
Residues for 17 pesticides were analyzed in 41 households in central New York State that represented farm, rural, and urban houses. Samples were taken in both summer and winter of 2000–2001 from the same households from four locations; family room carpet; adjacent smooth floor; flat tabletop surface; and settled dust collected in a Petri dish on a tabletop. Pesticide residues were analyzed to identity factors that influence both the transport into and the redistribution of pesticides in the indoor environment. Differences were observed between the various pesticides and pesticide classifications relative to location within and between households as well as by season. Variations in the pesticide residues were related to a number of factors. Higher residues were observed in the farm households, particularly in summer, with the highest amount observed for chloropyrifos in carpet (33 μg/m2). For many pesticides, the frequency of detection and the amount of residues were higher in summer, which relates to usage patterns in agriculture and horticulture; however, larger amounts of insecticides such as mecoprop, resmethrin, and tetramethrin were found on flat surfaces in winter, indicating household use and possible redistribution within the home. Distribution patterns suggest that routines within a household may cause high variation in residues; these practices include indoor pets and treatment for fleas and ticks, use of termiticides, and fastidiousness of occupants. Frequency of pesticide detection was highest in carpet for both summer and winter for all households, indicating that carpets hold pesticides over time. Adsorbent fibrous materials such as textiles hold pesticides by macro- and micro-occlusion in their complex structures. Amounts of pesticide residue were higher in carpets than on smooth floors, particularly for rural farm households where the farmer was a certified pesticide applicator. The maximum amount of pesticide residue on a smooth floor surface was 13.6 μg/m2 malathion while the maxima on wiped surfaces and in settled dust were 1.8 μg/m2 2, 4 D and 3 μg/m2 pendimethalin, respectively. Physical properties of individual pesticides such as vapor pressure influenced the distribution of the pesticide within the households. Evidence of volatilization of pesticides and redeposition on surfaces was observed, indicating that this is a mechanism for contamination of surfaces in addition to adsorption on airborne particles and tracking. High residues in winter are evidence that closure of households in winter that reduces ventilation results in redistribution of pesticides within households.
Butyltin Species in Benthic and Pelagic Organisms of the Saguenay Fjord (Canada) and Imposex Occurrence in Common Whelk (Buccinum undatum) by L. Viglino; É. Pelletier; L. E. J. Lee (pp. 45-59).
The distribution and accumulation of butyltins in various tissues of 13 benthic and pelagic species living in the sub-Arctic Saguenay Fjord (Canada) were investigated. Butyltin contamination was ubiquitous in this ecosystem with tributyltin (TBT) biota to sediment accumulation factors (BSAF) ranging between 0.22 and 11, but without any important biomagnification between trophic levels. The large range of butyltin compounds accumulating within different tissues of the species collected from all trophic levels was from 7 to 1238 ng Sn g−1 d.w. and indicates an exceptional contamination level only found in northern coastal areas exposed to an intensive traffic of commercial ships. Results show that bioaccumulation in organisms depends on three main factors: (1) the actual contamination level in their habitat, (2) their assimilation pathway by water, sediment or diet, and (3) their ability to metabolize TBT and excrete metabolites. By their lack of an efficient TBT degradation system, bivalves are subject to accumulate more butyltins (from 890 to 993 ng Sn g−1 d.w. for TBT and from n.d to 138 ng Sn g−1 d.w. for metabolites) whereas most burrow-dwelling organisms are able to degrade TBT and their butyltin levels ranged from 86 to 239 ng Sn g−1 d.w. for TBT and from 7 to 106 ng Sn g−1 d.w. for metabolites. Acadian redfish (Sebastes fasciatus) feeding preferentially on shrimps and small crustaceans rich in TBT showed a contamination level about three times higher than eelpout (Licodes vahlii). The latter species living in contact with the sediment and feeding on worms and other burrowing species had a lower proportion of TBT in their tissues. Finally, deleterious effects of butyltins in the Saguenay Fjord were assessed by the significant occurrence of Imposex in common whelk (Bucinum undatum) in two sites from Baie des Ha! Ha!. Results revealed that the effects of Imposex were accentuated close to the source of contamination, at Port-Alfred harbour, since the total of imposexed whelks collected at site A (the mouth of Baie des Ha! Ha!) was 12.5% and reached 52.6% at site B (Port Alfred). Although the incidence or frequency of imposex was low in site A compared to site B, the relative penile length index (RPL) values, a measure of the degree or severity of imposex, was similar at both sites indicating the presence of TBT with higher concentrations in site B.
Vanadium Distribution Following Decavanadate Administration by S. S. Soares; H. Martins; M Aureliano (pp. 60-64).
An acute exposure of two vanadate solutions—metavanadate and decavanadate—containing different vanadate oligomers, induces different patterns of subcellular vanadium distribution in blood plasma, red blood cells (RBC), and cardiac muscle subcellular fractions of the fish Sparus aurata (gilthead seabream). The highest amount of vanadium was found in blood plasma 1 h after (5 mM) intravenous vanadate administration (295 ± 64 and 383 ± 104 μg V/g dry tissue, for metavanadate and decavanadate solutions, respectively), being 80-fold higher than in RBC. After 12 h of administration, the amount of vanadium in plasma, as well as in cardiac cytosol, decreased about 50%, for both vanadate solutions. During the period between 1 and 12 h, the ratio of vanadium in plasma/vanadium in RBC increased from 27 to 128 for metavanadate, whereas it remains constant (77) for decavanadate. Both vanadium solutions were primarily accumulated in the mitochondrial fraction (138 ± 0 and 195 ± 34 ng V/g dry tissue for metavanadate and decavanadate solutions, respectively, after 12 h exposure), rather than in cytosol. The amount of vanadium in cardiac mitochondria was twofold higher than in cytosol, earlier for metavanadate (6 h) than for decavanadate (12 h). It is concluded that, in fish cardiac muscle, the vanadium distribution is dependent on the administration of decameric vanadate, with vanadium being mainly distributed in plasma, before being accumulated into the mitochondrial fraction.
The Effect of Creosote on Vitellogenin Production in Rainbow Trout (Oncorhynchus mykiss) by J. P. Sherry; J. J. Whyte; N. A. Karrow; A. Gamble; H. J. Boerman; N. C. Bol; D. G. Dixon; K. R. Solomon (pp. 65-68).
As part of a broader investigation into the effects of creosote treatments on the aquatic biota in pond microcosms, we examined the possible implications for vitellogenin (Vtg) production in Oncorhynchus mykiss [rainbow trout (RT)]. Vtg is the precursor of egg yolk protein and has emerged as a useful biomarker of exposure to estrogenic substances. Our a priori intent was to assess the ability of the creosote treatments (nominal cresoste concentrations were 0, 3, and 10 μl/L immediately after the last subsurface addition) to induce estrogenic responses in RT. The data showed no evidence of an estrogenic response in the treated fish. During the course of the experiment, however, the fish matured and began to produce Vtg, probably in response to endogenous estrogen. A posteriori analysis of the Vtg data from the maturing fish showed that after 28 days, the plasma Vtg concentrations were about 15-fold lower in fish from the creosote-treated microcosms compared with fish from the reference microcosm. Although the experiment design does not permit mechanistic insights, our observation suggests that exposure of female fish to PAH mixtures such as creosote can impair the production of Vtg with possible health implications for embryos and larvae.
Accumulation, Metabolism, and Food-Chain Transfer of Chlorinated and Brominated Contaminants in Subadult White Whales (Delphinapterus leucas) and Narwhals (Monodon monoceros) From Svalbard, Norway by H. Wolkers; C. Lydersen; K. M. Kovacs; I. Burkow; B. van Bavel (pp. 69-78).
The concentrations and patterns of polychlorinated biphenyls (PCBs), chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs) were studied in white whales (Delphinapterus leucas) and narwhals (Monodon monoceros) from Svalbard, Norway. In addition, their main food items were included in the study. In the whales, a broad range of pollutants was found in relatively high concentrations. PCBs and pesticides were approximately 3000 and 8000 ng/g lipid, respectively, for white whales and three times higher for narwhals. PBDEs 47 were approximately 70 ng/g lipid for white whales and 170 ng/g lipid for narwhals. Compared with other marine mammals from the same area, contaminant levels are among the highest levels ever measured. These high levels are likely in part because of a decreased capacity to metabolize contaminants. Metabolic indices indicated that most compounds accumulate to the same degree in white whales and narwhals, but for some toxaphenes and chlordanes, narwhals might have a decreased metabolism and consequently a higher accumulation. The three-times-higher contaminant levels in blubber of narwhals was further explained by substantially higher contaminant levels in their more benthic diet. The high levels and broad pattern of accumulating pollutants make white whales and narwhals excellent indicators for a wide range of contaminants in the Arctic.
Leachability of Protein and Metals Incorporated into Aquatic Invertebrates: Are Species and Metals-Exposure History Important? by Joseph S. Meyer; Michael J. Suedkamp; Jeffrey M. Morris; Aïda M. Farag (pp. 79-87).
To partially simulate conditions in fish intestinal tracts, we leached six groups of metals-contaminated invertebrates at pH 2 and pH 7, and analyzed the concentrations of four metals (Cd, Cu, Pb, and Zn) and total protein in the leachates. Four of the groups of invertebrates were benthic macroinvertebrates collected from metals-contaminated rivers (the Clark Fork River in Montana and the Coeur d’Alene River in Idaho, USA); the other two groups of invertebrates (one of which was exposed to metals in the laboratory) were laboratory-reared brine shrimp (Artemia sp.). Additionally, we fractionated the pH 2 leachates using size-exclusion chromatography (SEC). Protein content was 1.3 to 1.4× higher in Artemia than in the benthic macroinvertebrates, and leachability of metals and protein differed considerably among several of the groups of invertebrates. In SEC fractions of the pH 2 leachates from both groups of Artemia, Cu and protein co-eluted; however, Cu and protein did not co-elute in SEC fractions of the leachates from any of the benthic macroinvertebrate groups. Although none of the other three metals co-eluted with protein in any of the pH 2 leachates, one or more of the metals co-eluted with lower-molecular-weight molecules in the leachates from all of the groups of invertebrates. These results suggest fundamental differences in metal-binding properties and protein leachability among some invertebrates. Thus, different invertebrates and different histories of metals exposure might lead to different availability of metals and protein to predators.
Definition and Number of Subsamples for Using Mosses as Biomonitors of Airborne Trace Elements by J. R. Aboal; J. A. Couto; J. A. Fernández; A. Carballeira (pp. 88-96).
We collected 50 subsamples of the moss Scleropodium purum from each of three sampling sites and determined the concentrations of As, Cd, Cu, K, Hg, Ni, Pb, Se, and Zn in each subsample. We then calculated the number of subsamples required to determine significant differences in the mean concentrations of two sampling sites. We found that to differentiate between an uncontaminated sampling site and another, slightly contaminated site, 30 subsamples are required from each. On the basis of these results and because, to date, there are no studies that justify the application of the previously proposed recommendations, studies of local variability in other areas, and under different conditions, with other contaminants and moss species must be undertaken. For posterior comparison of data on variability as well as application of the recommendations associated with such results, the general use of a single definition of a subsample is required. We propose the following definition of a subsample: “1 g dry weight (approx.), collected within a 25-cm radius of a node, selected at random from a 1 × 1-m sampling grid placed in a sampling site.”
Trends of Chlorinated Organic Contaminants in Great Lakes Trout and Walleye from 1970 to 1998 by J. P. Hickey; S. A. Batterman; S. M. Chernyak (pp. 97-110).
Levels of chlorinated organic contaminants in predator fish have been monitored annually in each of the Great Lakes since the 1970s. This article updates earlier reports with data from 1991 to 1998 for lake trout (Salvelinus namaycush) and (Lake Erie only) walleye (Sander vitreus) to provide a record that now extends nearly 30 years. Whole fish were analyzed for a number of industrial contaminants and pesticides, including polychlorinated biphenyls (PCBs), dichloro-diphenyl-trichloroethane (DDT), dieldrin, toxaphene, and mirex, and contaminant trends were quantified using multicompartment models. As in the past, fish from Lakes Michigan, Ontario, and Huron have the highest levels of PCBs, DDT, and dieldrin; Superior has the highest levels of toxaphene; and Ontario has the highest levels of mirex. In the period after curtailment of chemical use, concentrations rapidly decreased, represented by relatively short half-lives from approximately 1 to 9 years. Although trends depend on both the contaminant and the lake, in many cases the rate of decline has been decreasing, and concentrations are gradually approaching an irreducible concentration. For dioxin-like PCBs, levels have not been decreasing during the most recent 5-year period (1994 to 1998). In some cases, the year-to-year variation in contaminant levels is large, mainly because of food-web dynamics. Although this variation sometimes obscures long-term trends, the general pattern of a rapid decrease followed by slowing or leveling-off of the downward trend seems consistent across the Great Lakes, and future improvements of the magnitude seen in the 1970s and early 1980s likely will take much longer.
Comparative Toxicokinetics of Cadmium in Artemia by R. Sarabia; I. Varó; F. Amat; A. Pastor; J. del Ramo; J. Díaz-Mayans; A. Torreblanca (pp. 111-120).
The toxicokinetics of cadmium was determined for five populations belonging to four species of Artemia (A. salina, A. parthenogenetica, A. franciscana, and A. persimilis) using a bicompartmental model. The effects of sublethal cadmium concentration on the kinetic parameters in A. parthenogenetica were determined. The BCF values are inversely related to the concentration, as is the uptake rate (ku), whilst the elimination rate (ke) constant seems to be directly related to the exposure concentration. Values corresponding to the rate of metal influx (I) remain relatively constant (0.2477 to 0.4455 μg/g.h) in the concentration range from 0.1 to 1 mg Cd/L, and are higher (1.098 μg/g.h) at an exposure to 10 mg Cd/L. The cadmium accumulation pattern seems well conserved in the genus and is characterized by a fast elimination of the metal with Ke ranging from 0.0050 to 0.0231 h−1. A. persimilis displays a different model to that corresponding to the other studied species exposed to the same cadmium concentration, presenting a low uptake rate constant (1.0564 mL/g. h) and a low BCF (211.3 mL/g).
Cadmium Accumulation and Antioxidative Responses in the Sesbania drummondii Callus by M Israr; S V Sahi; J Jain (pp. 121-127).
The effect of cadmium (Cd) on growth, accumulation, and antioxidative response was studied in Sesbania drummondii callus, cultivated on different concentrations of Cd (0–250 μM) for four weeks. Callus growth was comparable to that of the control for concentrations up to 50 μM Cd; however, concentrations higher than 50 μM affected growth. A concentration of 100 μM Cd inhibited growth by 16%, with respect to control. Cd concentration in callus increased with increasing Cd concentrations in the growth medium. Callus accumulated 530 mg Cd kg−1 of their dry weight at 100 μM Cd concentration. Sesbania callus responded to Cd-induced oxidative stress by modulating antioxidants (glutathione and other non-protein thiols) level and antioxidative enzymes: superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). The content of the glutathione (GSH) and GSH/GSSG ratio first increased up to a concentration of 50 μM Cd and then decreased. The content of other non-protein thiols significantly increased with increasing Cd concentrations in the growth medium. The activities of antioxidative enzymes, SOD, APX, and GR, followed the same trends as antioxidants first increasing up to a concentration of 50 μM Cd and then decreasing. These results suggest that antioxidative defense mechanisms play a significant role in Cd detoxification and accumulation in Sesbania drummondii.
Surfactant-Enhanced Desorption of Atrazine and Linuron Residues as Affected by Aging of Herbicides in Soil by M. S. Rodriguez-Cruz; M. J. Sanchez-Martin; M. Sanchez-Camazano (pp. 128-137).
In the present work, we studied the efficiency of two surfactants, one anionic (SDS) and other non-ionic (Triton X-100), in the desorption of atrazine and linuron after 0, 3, and 9 months of soil-herbicide aging time. Batch desorption studies were conducted in soil-water and in soil-water-surfactant systems. The kinetic pattern of desorption was biphasic, a slow desorption following an initial fast phase. Both phases followed first-order kinetics. The desorption rate of the first phase (K1) was very low in water for both herbicides and always increased in the presence of surfactants. At zero time, K1 increased 9- and 8-fold (atrazine), and 24- and 17-fold (linuron) in the presence of the two surfactants, respectively. Desorption rates decreased with the increase in the aging time in all three desorption systems. After 9 months of soil-herbicide aging time, DT25 for linuron was 6.85 h (SDS) and 41.7 h (Triton X-100) and for the atrazine it was only possible determine in SDS solution (17.2h). The amount of desorbed herbicide in the different systems varied from 35.6–12.5% (water), 87.9–46.2% (SDS), and 63.2–18.0% (Triton X-100) for atrazine and 8.02–3.94% (water), 69.9–41.3% (SDS), and 58.1–34.8% (Triton X-100) for linuron. The ratio of amount desorbed in surfactant solution and in water for the different aging times of the herbicides was greater for the desorption of linuron than that of atrazine. For both herbicides, it was always greater with SDS than with Triton X-100, and was higher when desorption of the residues aged for 9 months was carried out. The results indicate the interest of surfactants for increasing the desorption of atrazine and linuron from soils polluted with these compounds after a long aging time in the soil. Therefore, they indicate the possibility to use the pump-and-treat remediation technique for pesticides in soils with a long history of pollution. The enhanced desorption achieved will be governed by the hvdrophobic character of the herbicide, the nature of the surfactant used, the aging time, and the characteristics of soils.
Effect of Dislodging Techniques on Foliar Residue Determination for Agricultural Crops by E. Bruce; S. Korpalski; D. Johnson; D. Klonne; W. Nagel; L. Holden; B. Lange (pp. 138-143).
The Agricultural Reentry Task Force (ARTF) conducted a study to determine whether different dislodgeable foliar residue (DFR) techniques had any effect on the amount of residues dislodged from the leaves of vegetable crops. Four previously employed techniques were evaluated with two chemicals (carbaryl and methomyl) on two crops (cabbage and lettuce). Carbaryl, a moderately water-soluble chemical, was applied at a rate of 2.0 lbs active ingredient/acre (lb ai/A) while methomyl, a highly water soluble chemical, was applied at a rate of 0.9 lb ai/A. One day after application, leaf punches were collected and the residues were dislodged following one of four techniques that differed in the number of dislodgings per sample, the duration of dislodging, the solution volume, and/or the type of solution used. The results indicated that three of the techniques gave similar results, whereas a fourth gave marginally lower results.
Mode of Action and Growth Toxicity of Arsenic to Tilapia Oreochromis mossambicus Can Be Determined Bioenergetically by J W Tsai; C.-M Liao (pp. 144-152).
We present a bioenergetics-based approach to analyze the chronic effects and growth toxicity mode of action in tilapia Oreochromis mossambicus exposed to waterborne As and to predict fish growth under different exposure scenarios. 7-day exposure bioassays showed that tilapia accumulate As when exposed to waterborne As. We conducted growth bioassays to assess chronic As toxicity to tilapia. We incorporated a universal ontogenetic growth model with the DEBtox theory to explore the mode of action of As toxicity. Our results show that the specific growth rates of exposed tilapia are inversely proportional to As concentrations and are calculated as 0.76% d−1 in 0 μg mL−1, 0.57% d−1 in 1 μg mL−1, 0.2 % d−1 in 2 μg mL−1, and 0.04% d–1 in 4 μg mL−1 As, respectively. We showed that the internal threshold concentration did not change significantly with time, demonstrating that the critical body residue approach is applicable for As toxicity assessment. We distinguished between three modes of action of As, including direct effects on growth and indirect effects by way of maintenance and food consumption. Our results support that decreased feeding accounts for the growth decrease in the case of feeding ad libitum. The feeding decrease model also illustrates the growth trajectories of tilapia during the entire whole life span, suggesting that the maximum biomass of tilapia are 1038.75 g in uncontaminated water and 872.97 g in 1 μg mL−1, 403.06 g in 2 μg mL−1, and 336.65 g in 4 μg mL−1 As, respectively. We suggest that considering modes of action in ecotoxicology not only improves our understanding of the toxicities of chemicals, it is also useful in setting up models and avoiding pitfalls in species- and site-specific environmental risk assessment. This proposed framework for tilapia gives preliminary information relevant to aquacultural and ecologic management.