Abstract:The indiscriminate use of pesticide is a treat to non-target organisms. This study evaluates the haematological and biochemical changes induced by inhalation of local Nigerian dichlorvos insecticide on rats. The rats were randomly assigned to a control group which received only food and water and a test group which, in addition to food and water, was exposed to the pesticide for a period of 4 h daily for 28 days, after which exposure was discontinued for seven days. Five animals were sacrificed from each group on days 1, 7, 14, 21, 28 and 35, and blood was collected by cardiac puncture for haematological, biochemical and antioxidant analysis. Results obtained showed lowered values of red blood cell count (RBC), packed cell volume (PCV), haemoglobin, mean cell haemoglobin (MCH) and mean cell haemoglobin concentration (MCHC) (p < 0.05) with increased white blood cell count (WBC) and platelet counts after day 14 when compared to the control group. Liver enzymes aspartate amino transaminase (AST) and alanine amino transaminase (ALT) were higher in the exposed rats compared to the control group (p < 0.05). Urea and creatinine concentrations increased significantly after day 1 and at day 28, while superoxide dismutase (SOD), gluthathione (GSH) and catalase (CAT) activity increased significantly compared to the control after day 1, day 14 and day 21, respectively. The RBC, PCV and haemoglobin values of all exposed rats were restored to normal following withdrawal of the pesticide, though AST, ALT, urea, creatinine and, glutathione values remained significantly high compared to the control. Inhalation of the local insecticide is toxic to the blood, liver and kidney of laboratory rats and may be deleterious to human health following long-term exposure.

Aquatic organisms are often exposed briefly to high pesticide concentration. Survival time model was used to study risk of death in C. gariepinus and O. niloticus fingerlings exposed to 24 mg/L atrazine, 42 mg/l mancozeb, 1 mg/L chlorpyrifos and 0.75 µg/L lambda cyhalothrin for 15, 30, 45 and 60 minutes and continuously for 96 hours. Mortality, time-to-death, weight, length, and condition factor of the fingerlings were recorded. Results obtained showed tilapia was more susceptible than catfish to continuous exposure but not pulse exposure. The survival probability of both species was similar when exposed for 15, 30 and 45 minutes (p > 0.05) but differed after 60 minutes (p < 0.05). Risk of death of catfish exposed briefly to atrazine, mancozeb and chlorpyrifos for 60 minutes was similar to 96 hours continuous exposure, same for tilapia exposed to 1 mg/L chlorpyrifos (p > 0.05). Survival probability of tilapia exposed to chlorpyrifos for 15, 30, 45 and 60 minutes was similar (p > 0.05) and was not influenced by pulse length. Pesticide hazard and risk of death decreased as fish size (weight, length, and condition factor) increased. Pulse toxicity assessment using survival models could make pesticides exposure assessment more realistic by studying factors that can influence the toxicity of pesticides.

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Background Pulse exposures are the consequences of the intermittent release of pollutants in the environment. Brief exposure of aquatic organisms to high concentrations of pesticides simultaneously occurs, particularly in small watercourses during high flows. The effects of pulse exposure often include effects occurring during and after the exposure. Despite this, routine toxicity tests procedures often ignore brief exposure scenarios and the role of time in toxicity. We conducted a pulse toxicity test by briefly exposing African catfish and Nile tilapia fingerlings to pesticide mixtures of atrazine, mancozeb, chlorpyrifos, and lambda-cyhalothrin. The study aimed to estimate pesticide mixture interaction in pulse-exposed fish and elucidate the influence of species differences on the response of fish to the pesticide mixture. Results Despite the similarity in fingerlings weight, African catfish had a significantly higher survival probability than Nile tilapia after exposure to atrazine-mancozeb mixture. However, the survival probability of African catfish and Nile tilapia fingerlings were similar after exposure to atrazine-chlorpyrifos, atrazine-lambda cyhalothrin, mancozeb-chlorpyrifos, mancozeb-lambda cyhalothrin, chlorpyrifos-lambda cyhalothrin, and quaternary mixture (p > 0.05). The survival probability of exposed fingerlings was significantly lower for continuous than pulse exposure to the mixtures (p < 0.01). Nevertheless, the survival probability of 60 min of pulse exposure to 13.49 mg/L mancozeb-lambda cyhalothrin was similar to continuous exposure for 96 h. Atrazine-mancozeb, atrazine-chlorpyrifos, atrazine-lambda cyhalothrin, mancozeb-chlorpyrifos, mancozeb-lambda cyhalothrin, and the quaternary pesticide mixture were antagonists in African catfish but not in Nile tilapia. At the same time, chlorpyrifos-lambda-cyhalothrin was antagonistic in Nile tilapia but not African catfish. Conclusions Pesticide mixture interaction was antagonist but specie-dependent. Innate intrinsic and extrinsic deterministic factors and, to a limited extent, stochastic processes may have influenced the survival probability of African catfish, and Nile tilapia pulsed exposed to complex pesticide mixtures. Pulse toxicity assessment using survival analysis is relevant in ecotoxicology as it enables the study of factors that can influence pulse toxicity.

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In this paper, we present an integrated workflow utilizing a numerical model to identify optimal operating envelope for horizontal wells producing from dual permeability media. A synthetic dual permeability numerical model comprised of critical components namely: fracture and matrix permeabilities, matrix-fracture conductivity (shape factor), and fracture distribution based on Discrete Fracture Network (DFN) scheme was built. In addition, two horizontal producers completed with Inflow-Control – Devices (ICDs) and as open-hole respectively, are also connected to the model. Rigorous sensitivity analysis is implemented on these key parameters using the dynamic model under Equalspacing sampling scheme with well oil rate as the objective function. Range of values on each variable are typical for naturally fractured reservoirs. In addition, detailed sensitivity on ICD parameters such as flow resistance ratings are performed. Results from the analysis are presented in cumulative probability function identifying most likely, pessimistic and optimistic values. Among all the variables, Matrix-fracture transmissibility has most impact. Unfortunately, it is often neglected when designing horizontal wells in dual permeability reservoirs. Current practice pays most attention on permeability contrast lack of consensus in the industry on best technique for its estimation. Most common methodologies applied are Kazemi and Warren-Roots. Nevertheless, it plays a critical role in describing dual permeability subsurface flow mechanism. Most significantly, it is widely acknowledged that beaning up choke sizes enhances production performance of wells connected to dual permeability. However, in this study, we have been able to establish operating limits for this phenomenon. Matrix-fracture transmissibility could significantly influence a producer, which has not intersected high permeability streaks. Our study clearly demonstrates this observation using high-resolution dual permeability dynamic model. In addition, by performing multi-variate characterization, we establish operating envelope for optimizing well production performance in dual media systems through choke size settings.

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