Dichlorvos as a residual fumigant in mud, plywood and bamboo huts

In experiments conducted at Savannah, Ga., dichlorvos dispensers of montan (lignite) wax installed at a rate of six units per 1000 cubic feet (28 m³) in huts with mud or bamboo walls and with thatched roofs produced kills of caged Anopheles quadrimaculatus (12 hours'' exposure) at or above 95% for 5-6 weeks. The doors, windows, and eaves of the huts were open for maximum ventilation. In a non-ventilated plywood hut, a single dispenser gave effective kills for 7 months but in a non-ventilated mud hut the period was 5 months. Air concentrations of dichlorvos in the mud hut were shown to be definitely lower than those in a plywood hut at the same dosage level.     

Assessment of the kill of Anopheles gambiae by the fumigant insecticide dichlorvos in experimental huts

As part of the World Health Organization''s programme for the evaluation and testing of new insecticides, different types of dichlorvos dispenser were installed in experimental huts in Tanganyika for study of their effectiveness in killing Anopheles gambiae. It was found that satisfactorily high mosquito mortalities of 75% or more were maintained for one to two months after installation of a dispenser. Mortalities were about 10% higher in huts with grass roofs than in those with mud-lined roofs. The vapour toxicity was similar in the two types of hut, but the results of bio-assay tests on different types of surface showed that there was a residual contact effect of the insecticide as well as the fumigant effect; the lower mortalities in the mud-roofed huts may be due in part to removal or decomposition of the dichlorvos by the mud surface.     

A large-scale field trial with dichlorvos as a residual fumigant insecticide in Northern Nigeria

An extended field trial with dichlorvos was carried out in the Kankiya District of Northern Nigeria during 1963. Two types of dispenser were used—the dichlorvos-impregnated-montan-wax type and the liquid-dichlorvos type. The objective of the trial was to see if dichlorvos would interrupt the transmission of malaria under local conditions when used at a dosage of one dispenser per 15 m³ of living space. On the basis of epidemiological findings—both parasitological and entomological—it was found that, owing to excessive ventilation in the huts treated, an adequate concentration of dichlorvos was not maintained, and transmission continued uninterrupted.     

Observations on the effect of residual insecticides in experimental huts in Masaka District, Uganda

Observations made in Kigezi District, Uganda, had shown a great reduction in the number of Anopheles gambiae entering an experimental hut treated with DDT. The work reported in this paper confirms the phenomenon of reduced entry by A. gambiae and A. funestus in two experiments carried out in Masaka, another district of Uganda, using mud-walled huts, roofed with thatch or corrugated-iron sheets and sprayed with DDT and dieldrin. The fact that no similar reduction was observed with Mansonia (mansonioides) uniformis, a common species in the area, indicates the need to determine and take into account any reduction in the number of entering mosquitos when assessing the effect of residual insecticides. Of interest in these experiments was the finding that DDT and dieldrin produced satisfactory kills with all the local anopheline species in spite of their rapid sorption by the mud walls, an indication of the importance of thatch or metal roofs as a source of active insecticide.     

An evaluation of the residual lifespan of DDT in malaria control

The insecticide lifespan of DDT was assessed in huts sprayed for malaria control. The age of the spray deposits ranged from 3 up to 22 months. Blood-fed female Anopheles arabiensis were either released into the huts or exposed on sprayed surfaces by a bioassay technique. Mosquitoes released were recovered in exit traps fitted on windows or dead on the floor. Only 50% or less of mosquitoes released in sprayed huts were recovered. Mortality figures for recovered mosquitoes ranged from 94% at 3 months, declining to 19% for huts sprayed 18 months previously. Of the recovered mosquitoes, 60% or more attempted to escape from sprayed huts within two hours postrelease up to 15 months postspray. Bioassays gave average mortalities of 95 and 76% on thatch and mud walls, respectively. Analysis of mud samples from test huts showed that target dose of 2 g AI/m2 of DDT was not being achieved. The results support the need for an annual spraying cycle.     

Evaluation of synthetic repellents on mosquito nets in experimental huts against insecticide-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes

Owing to the development of pyrethroid resistance in Anopheles gambiae, there is a need to develop chemical alternatives for use on mosquito nets. Synthetic insect repellents are widely used for personal protection as skin or clothing applications. The efficacy of repellent-treated nets (RTN) was evaluated in experimental huts in C?te d'Ivoire against pyrethroid-resistant populations of An. gambiae and Culex quinquefasciatus. The repellents tested were DEET (N,N-diethyl-3-methylbenzamide) at 7.9 g/m2 and two formulations of ethyl butylacetylaminopropionate (IR3535) at 7.6 g/m2 and 7.3 g/m2. Over 45 nights there was a 74-82% reduction in the number of An. gambiae entering the huts containing RTNs but no significant reduction in entry of C. quinquefasciatus. There was a 63-64% reduction in the proportion of An. gambiae blood feeding but no reduction in the proportion of C. quinquefasciatus blood feeding in huts with RTNs. An unexpected result was the 69-76% mortality of An. gambiae and 51-61% mortality of C. quinquefasciatus in huts containing RTNs. Treated filter paper bioassays in WHO test kits confirmed that confined contact with DEET induces mortality. The DEET-based product provided better and longer protection; tunnel test bioassays confirmed that residual activity lasted for up to 6 weeks. Application of repellents to nets warrants further investigation and development.     

Acute Toxicity and Acetylcholinesterase Inhibition in Grass Shrimp (<Emphasis Type="Italic">Palaemonetes pugio</Emphasis>) and Oysters (<Emphasis Type="Italic">Crassostrea virginica</Emphasis>) Exposed to the Organophosphate Dichlorvos: Laboratory and Field Studies

The use of various organophosphates to control mosquito populations is a common practice across the globe. We review the literature (LC50s) on dichlorvos, the primary breakdown product of Dibrom, and use laboratory and field experiments to determine the lethal and sublethal (bioassays) effects of dichlorvos on two widely distributed and ecologically important estuarine invertebrate species, the marsh grass shrimp, Palaemonetes pugio and the Eastern oyster, Crassostrea virginica. Laboratory results based on LC50s and sublethal acetylcholinesterase (AChE) inhibition activity bioassays indicate that adult grass shrimp are more sensitive (approximately 500 x ) to dichlorvos than juvenile oysters. Although potentially an important factor for intertidal or shallow-dwelling estuarine organisms, the toxicity of dichlorvos was not enhanced in the presence of simulated sunlight for adult P. pugio. The most notable decreases in AChE activity were for grass shrimp and oysters exposed to dichlorvos concentrations above those considered ecologically relevant. In field experiments, both species were deployed in cages in unsprayed (n = 2) and sprayed (n = 3) sites and water samples collected pre- and post-spraying. Quantifiable dichlorvos levels were measured at the two narrowest creek treatment sites following mosquito spraying, suggesting that overspray can occur and there was evidence of a sublethal AChE response at these same sites. However, experiments at the widest creek revealed no measurable dichlorvos or sublethal responses. Results from this research suggest that adult grass shrimp are more sensitive to dichlorvos than juvenile oysters. Spraying near small tidal creeks may have measurable impacts on resident species, while larger (wider) creeks appear to be capable of buffering organisms from transient fluxes of mosquito control agents that may enter the system.     

Field measurement of the effective dominance of an insecticide resistance in anopheline mosquitos

Anopheles culicifacies that were susceptible, heterozygous, or homozygous resistant to HCH and dieldrin were differentially marked with fluorescent dusts and released twice weekly into village huts in Pakistan that had been sprayed with four different dosages of HCH to see which of the genotypes died and which survived. The three highest dosages killed all three genotypes in the first four weeks, and heterozygotes and susceptibles for at least 12 weeks. The lowest dosage killed all the susceptibles throughout the period, and all but 0.07% of the heterzygotes. Thus the resistance is effectively recessive at the higher dosages and unlikely to be selected rapidly, as long as the gene frequency is low to start with and the houses are sprayed regularly. Similar releases of partially and completely resistant A. stephensi, and completely resistant A. subpictus, showed greater survival rates on exposure to the high HCH dosages than the same genotypes of A. culicifacies.     

Determination of airborne concentrations of dichlorvos over a range of temperatures when using commercially available pesticide strips in a simulated military guard post

Dichlorvos is a chemical compound which has been used for decades as a pesticide. Potential inhalational exposure to dichlorvos vapor associated with using commercially-based, dichlorvos-impregnated resin strips in a simulated military guard post was evaluated. A varying number of these pesticide strips, ranging from the manufacturer's guidelines ((3)-16 g strips) up to a full package of strips ((12)-16 g strips), were placed in a small, enclosed space (2.31 m x 2.26 m x 2.44 m, 12.7 m³), which was similar in size to a typical military guard post. Static air sampling was then conducted to simulate personal air sampling, followed by analysis using OSHA Method 62 (GC-ECD). Air sampling was conducted over a range of discrete temperatures (26–38?C) which approximated average ambient temperatures expected in a variety of deployed environments. Air sampling in this range was conducted to determine the airborne concentration generated at each temperature setting. Airborne concentrations were then compared to established short term military exposure guidelines (MEGs) and the 8-hr OSHA permissible exposure limit (PEL) for dichlorvos (both criteria limits are 0.99 mg/m³). Results from air sampling indicated that exceeding the manufacturer-recommended number of strips for the workspace volume and environmental conditions produced airborne dichlorvos concentrations above established occupational standards (1.77–3.70 mg/m³). Such exposures may potentially lead to adverse effects, such as loss of mental and visual acuity for guard post watch standers who employ more strips within a space than recommended per the manufacturer for the size of the space. However, concentrations of airborne dichlorvos generated when adhering to manufacturer's guidelines based on workspace volume resulted in levels of 0.16–0.39 mg/m³ for 1-hr and 8-hr timeframes, which were below the established occupational health limits. While dichlorvos-impregnated strips are not currently recommended for use in manned workspaces for periods > 4 hr, findings suggest that prolonged use (8 hr) of similar pesticide strips within manned spaces to repel and/or kill disease-carrying insects may be possible without experiencing adverse health effects.     

Safety Evaluation in the Home of Polyvinyl Chloride Resin Strip Containing Dichlorvos (DDVP)

In a period of two years a series of three-home studies involving 26 families in Arizona was conducted to further evaluate the safety of the dichlorvos (DDVP)- containing insecticide strip. Physical examination, hematologic and clinical chemistry measurements, blood cholinesterase assays, and analysis of air and food for dichlorvos were carried out. Exposures were designed to be exaggerated in that strips were used throughout the homes (averaging 7 to 11 per home) and replaced with fresh ones, either every three months for one year or monthly for six months.

Throughout the studies, all examinations and measurements revealed no adverse effect on health. The red cell cholinesterase activity also remained unaffected. A slight plasma cholinesterase depression of no toxicological importance was observed in the study where the strips were replaced monthly over six months.

In homes containing 8 to 18 strips, maximum air and food concentrations of dichlorvos averaged approximately 0.13 mg/cu m and 0.12 ppm, respectively.     

Evaluation in test huts of the protective effects of untreated mosquito nets against Anopheles gambiae s.s. bites

The protection against insect bites afforded by untreated mosquito bed nets was studied at the field stations of Yaokoffikro and M'bé in Ivory Coast. We tested damaged mosquito nets (tear holes covering 0.8% of the total area) in Yaokoffikro, undamaged mosquito nets and huts without mosquito nets in M'bé. The blood feeding rate of Anopheles gambiae was 70% lower in huts with undamaged mosquito nets than in huts with no mosquito net or a damaged mosquito net. The natural exophilic behavior of the mosquito was increased and mosquito mortality reached 7.4%. The blood feeding rate of An. gambiae was 83% in huts with no mosquito net and 68% in huts with damaged mosquito nets. Exophilic behavior was normal (25%) and overall mortality was 5%. Immediate mortality of An. gambiae was 54% with undamaged mosquito nets and only 17% in huts with no mosquito net. This difference may reflect the state of nutrition of the mosquitoes: 86% of the dead mosquitoes found in huts with undamaged mosquito nets had not fed, versus only 24% in huts with no mosquito net. The unfed mosquitoes may be considered to have died from starvation. Intact mosquito nets conferred some protection against An. gambiae. This protection was not total but was "better than nothing", with 25% of mosquitoes blood feeding effectively even in the presence of an intact mosquito net. This protection reduces the probability of survival of the females. In contrast, torn mosquito nets trap the mosquitoes that enter, then allowing more than two thirds of the mosquitoes to take a blood meal on the sleeper.     

Radioactive cesium in dirt accumulations on the roof of buildings.

The concentrations of 137Cs and 134Cs in dirt deposits on the roofs of buildings are much higher than those in the surface of soil at ground level. Thus dirt on roofs concentrates radioactive cesium in fall-outs. The 137Cs concentration in dirt deposits on the roofs of older buildings is not consistently higher than that on the roofs of new ones, but the 137Cs/134Cs ratio is higher in deposits on older buildings constructed before the first half of the 1970s, and decreases exponentially with decrease in age of the buildings gradually reaching 1.9 +/- 0.2, the value in the air-borne dust at the time of the Chernobyl accident. From this relationship, the contribution of Chernobyl radioactivity to accumulated 137Cs was calculated as 32% on buildings constructed in 1962. The radioactive cesium concentrations in dirt deposits in gutters of private houses and on the roofs of university buildings in Japan were also determined.     

Selective and conventional house-spraying of DDT and bendiocarb against Anopheles pseudopunctipennis in southern Mexico

Indoor feeding behaviors and mortalities of Anopheles pseudopunctipennis females were evaluated following contact with selective (bands covering mosquitoes' preferred resting areas) and full applications of DDT and bendiocarb on indoor sprayable surfaces. The DDT residues provoked strong avoidance behavior. To a lesser degree, mosquitoes were also repelled by bendiocarb-sprayed surfaces. Because of strong irritancy/repellency, unfed mosquitoes were driven outdoors in proportionally higher numbers. The resting time on selectively or fully DDT-sprayed huts was greatly reduced in comparison to bendiocarb-sprayed huts. Although unfed mosquitoes tended to rest on non-DDT-sprayed surfaces in the selectively treated hut, the man-biting rate was similar with both types of treatments. Unfed mosquitoes were repelled less from selectively bendiocarb-treated surfaces. Similar reductions in postfed resting times were observed on all surfaces suggesting that once fed, mosquitoes rested on sprayed surfaces for shorter intervals of time. Engorged mosquitoes had normal resting behavior (pre- and postspray) within the range of preferred resting heights in both DDT- and bendiocarb-sprayed huts, but the proportion of mosquitoes fed in the DDT-treated huts was lower. Selective spraying of walls was as effective as spraying the complete walls with both insecticides, but DDT was more effective in reducing mosquito-human contact. These studies show that by more effectively targeting vector behavior, a cost-effective alternative to traditional control techniques can be achieved.     

Effects of dichlorvos and carbaryl on the activity of free and immobilized acetylcholinesterase

Acetylcholinesterase (AChE) is responsible for the rapid hydrolytic degradation of the neurotransmitter acetylcholine into inactive products choline and acetic acid. The purpose of this study was to examine the effect of carbaryl and dichlorvos on the activity of AChE. In this experimental study, 60 samples of free and immobilized form of AChE were prepared. Determination of AChE activity followed the Ellman's method with modifications. Briefly, 200 μl of the enzyme solution was combined with 400 μl of 25 mM phosphate-buffered saline, 200 μl of DTNB [5,5'-dithio-bis(2-nitrobenzoic acid)], and 200 μl of 300 μM acetylthiocholine iodide. Triplicate (1000 μl) samples were transferred to clean 1.5-ml centrifuge tubes, mixed, and held on ice until analysed and the change in absorbance was measured. For inhibition studies, substrate solutions were pre-incubated with dichlorvos and/or carbaryl. Dichlorvos and carbaryl were used at the concentrations of 100 and 500 μM. The activity was evaluated at 412 nm using Ceceil, CE 1020 spectrophotometer. Phosphate buffer (pH 7.35) was used for blanks. AChE activity was quantified as mM/ml/min. AChE activity of free form is more affected by Dichlorvos (0.09 ± 0.03 mM/ml/min) than immobilized form (0.19 ± 0.02 mM/ml/min). AChE activity of free form is more affected by carbaryl (0.11 ± 0.01 mM/ml/min) than immobilized form (0.1 ± 0.04 mM/ml/min). Comparison of mean AChE activity showed that the activity of the enzyme in presence of dichlorvos and carbaryl was significantly lower compared to controls. To calculate the significance of the difference, the t-test for paired values was applied. The results of our study indicate that dichlorvos and carbaryl cause decrease in AChE activity for both free and immobilization form of enzyme. It is therefore concluded that measuring AChE activity is a way to evaluate poisoning with carbaryl and dichlorvos.     

Effect of DDT on survival and blood feeding success of Anopheles arabiensis in northern Kwazulu, Republic of South Africa

The effect of house spraying with DDT on blood-feeding and resting behavior of An. arabiensis in Natal Province, Republic of South Africa, was investigated. Indoor resting occurred in both control (unsprayed) and replastered (DDT on walls covered due to replastering) huts, but was minimal in fully DDT-sprayed huts. The percentage of bloodfed mosquitoes was greater than 50% in both control and replastered huts, but in the latter huts there was a reduction in the percentage of gravid and an increase in the percentage of unfed mosquitoes. Large numbers were collected in exit traps irrespective of the DDT status of the huts. The percentage of catch that was bloodfed was lowest in exit traps fitted on DDT-sprayed houses. The percentage survival of bloodfed mosquitoes caught in exit traps exceeded 72% for all 3 hut types. The survival of unfed mosquitoes was, however, markedly lower. Susceptibility tests showed no physiological tolerance to DDT by the wild An. arabiensis population. Bioassays using colonized An. arabiensis showed the DDT deposits on hut walls to effect 100% kill with 15 minutes of exposure.     

敌敌畏对大鼠脑组织N-甲基-D-天门冬氨酸受体活性的影响

目的 研究敌敌畏(DDVP)染毒后大鼠脑组织中N-甲基-D-天门冬氨酸(NMDA)受体的变化规律,探讨其在有机磷农药中毒中的作用。方法 55只雄性SD大鼠分为11组,每组5只,一组为生理盐水(NS)组,高剂量组(25mg/kg)和低剂量组(15mg/kg)各5组,染毒组分别以敌敌畏腹腔注射,染毒后4h、8h、16h、24h、48h处死,测定大鼠全血和脑组织的乙酰胆碱酯酶(AChE)活性以及脑组织中NMDA受体的活性。结果 DDVP染毒后大鼠全血和脑组织的AChE活性显著下降,且脑组织AChE活性下降更多,抑制率大于80％,恢复更迟缓。脑组织中NMDA受体的最大结合容量(Bmax)在4h便明显下降,于24h达到最低,然后逐渐升高,受体的平衡解离常数(Kd)在4h时明显上升,于24h达到最高,然后逐渐下降。结论 DDVP染毒对大鼠脑组织AChE活性抑制严重,说明中枢神经系统对DDVP的毒作用敏感。同时DDVP染毒对大鼠脑组织中NMDA受体产生下降调节,表现为受体数量减少、亲和力降低。推测这是机体的一种自身调节机制,可减少过度刺激并保护中枢神经系统。     

N6-环戊基腺苷治疗敌敌畏急性中毒的实验研究

目的研究腺苷受体激动剂N6-环戊基腺苷(CPA)对急性敌敌畏(DDV)中毒的疗效和作用机制.方法小鼠和大鼠用DDV灌胃染毒后,经腹腔注射生理盐水、CPA、阿托品(At)、氯解磷定(PAM-Cl),观察各组动物中毒表现和死亡结局,测定DDV染毒大鼠CPA治疗和未治疗组全血胆碱酯酶(ChE)活力及乙酰胆碱(ACh)含量.结果(1)CPA等治疗组动物与未治疗组相比,中毒表现出现时间延迟、中毒程度减轻、存活率提高;(2)CPA治疗组大鼠全血ChE活力[(0.49±0.05)U/ml]和未治疗组大鼠[(0.52±0.04)U/ml]均比对照组大鼠[(1.56±0.15)U/ml]明显降低,差异有统计学意义(P＜0.01),但治疗组与未治疗组的差异无统计学意义(P＞0.05);(3)CPA治疗组大鼠全血ACh含量[(204.24±20.48)μg/ml]比未治疗组大鼠[(230.91±25.61)μg/ml]明显降低,差异有统计学意义(P＜0.05).结论CPA对急性DDV中毒有治疗作用,这种作用主要是通过减少ACh的量来实现的.     

Effect of dichlorvos on the acetylcholinesterase from tambaqui (Colossoma macropomum) brain

Dichlorvos is an acutely toxic organophosphorous pesticide that is known as a classical acetylcholinesterase (AChE; EC 3.1.1.7) inhibitor. Here, the brain AChE from the important Amazonian fish tambaqui (Colossoma macropomum) was assayed in the presence of this insecticide and also of deltamethrin, a classical sodium and potassium channel inhibitor (negative control). Four tissue homogenates were analyzed in triplicate for AChE activity using acetylthiocholine as the substrate and 5,5'-dithiobis(2-nitrobenzoic) acid (DTNB) as the color-developing agent. Each tissue homogenate represented pooled brains from five fish. The inhibitory effect of dichlorvos on AChE activities was determined at concentrations from 0.001 to 10 ppm and compared to controls. This effect followed an exponential decay model (y = 9.420 + 26.192e(-x/5.380); r2 = 0.989), presenting IC50 (the concentration of dichlorvos that is required for 50% of AChE inhibition) of 0.081 ppm (0.368 micromol/L). No effect was observed for the deltamethrin, and the concentration 0.0452 micromol/L of dichlorvos was significantly different from this control. These results suggest that tambaqui brain AChE can be proposed as a biomarker for dichlorvos and can be used as a tool for aquatic environment monitoring.     

A village-scale trial of fenthion as a residual spray in Nigeria

In the course of an insecticide-testing programme, fenthion was applied in mud-walled huts at an intended concentration of 1.5 g/m² in a village near Lagos, Nigeria. This paper describes the entomological results obtained. Bio-assays on Anopheles gambiae showed an effective kill (i.e., over 70%) for 7 weeks on mud surfaces, 11 weeks on wood surfaces and 16 weeks on raffia-palm mid-ribs. No mosquitos were found in pyrethrum spray catches in the treated village for 7 weeks after the application of fenthion, although low numbers persisted in the control village near by.     

本溪市垃圾转运站发展的实践与探讨

本溪市自１９９４年起建设了约１００座垃圾房。通过对几种垃圾收运方式的比较，结合本溪市的实际情况确定以建设垃圾屋为主，逐渐开展居民生活垃圾袋化收集的方式，在新建小区的环卫验收时，要验收是否建设了配套的垃圾房，从而解决了垃圾房的建设资金问题，使环境卫工作得到发展。