Field-collected Water Samples Research Articles

Comparative study on the larvicidal effect of some ciliated protists on Culex gelidus, Culex tritaeniorhynchus, and Aedes aegypti in Sri Lanka

Rice fields in Sri Lanka create suitable breeding places for vector mosquitoes. Such sites provide habitats for diversified naturally occurring microbiota. Ciliated protists, Zoothamnium sp., Chilodonella sp., and Vorticella microstoma are among such microbiota found in vector mosquito habitats especially in rice field habitats in Sri Lanka. The present study was carried out to determine the comparative larvicidal effect of these ciliated protists collected from naturally infested mosquito larvae in some rice-field habitats in Kurunegala, Sri Lanka, against vector mosquito larvae. Vector mosquito larvae, Culex tritaeniorhynchus, and Culex gelidus were reared in the laboratory from field-collected water samples while Aedes aegypti mosquito larvae were reared using egg sheets, for the laboratory bioassays. V. microstoma showed the potential for infection and mortality of Cx. tritaeniorhynchus larvae (71.33% ± 5.23). Results revealed a minimum of 1000V. microstoma is required to kill a single third instar larva of Cx. tritaeniorhynchus at 69.60 ± 2.40h of exposure. Cx. gelidus larvae showed 41.33% ± 3.43 mortality due to V. microstoma infestation. However, none of the ciliates were effective against Ae. aegypti larvae. Chilodonella sp. was very occasionally reported during this study hence was not possible to the mass rear for experimentations. This study concludes that V. microstoma is an effective ciliated parasite of Cx. tritaeniorhynchus larvae. Due to their effectiveness and eco-friendly nature, this species can be developed as an effective bio-controlling agent against Cx. tritaeniorhynchus mosquito species.

Water quality assessment in mosquito breeding habitats based on dissolved organic matter and chlorophyll measurements by laser-induced fluorescence spectroscopy.

Rapid urbanization and its associated pollution can affect water quality in mosquito breeding habitats and, as a result, the ecology and control of mosquito vectors. To understand the effects of pollution on mosquito vectors, an accurate assessment of water quality in breeding habitats is needed. Presently, water quality assessment of mosquito breeding habitats is usually based on the measurement of individual physicochemical parameters. However, several parameters are sometimes difficult to interpret or may not give a clear picture of the overall water quality of the breeding habitats, especially when the pollutants are in complex mixtures. This study employed the use of Laser-Induced Fluorescence (LIF) spectroscopy to assess water quality in breeding habitats of Anopheles, Aedes, and Culex mosquitoes in urban areas in Cape Coast, Ghana. The LIF spectra, using a 445-nm diode laser, were measured from field-collected water samples in the laboratory. The LIF spectra showed the presence of dissolved organic matter (DOM) and chlorophyll in the breeding habitats. The DOM and chlorophyll fluorescence signals were normalised by the Raman vibrational signals to determine water quality in each habitat. The overall water quality was better in Aedes breeding habitats than in Anopheles and Culex breeding habitats. The poor water quality in Anopheles and Culex breeding habitats was due to the presence of high fulvic acid and chlorophyll content, which often reflect pollutants from anthropogenic sources. Anopheles and Aedes habitats were made up of mainly An. coluzzii and Ae. aegypti respectively while Culex species were identified to genus level. The results add up to the growing concern about the breeding of Anopheles in polluted habitats. The study demonstrated for the first time the ability of LIF spectroscopy to assess water quality in mosquito breeding habitats.

Karenia brevis bloom patterns on the west Florida shelf between 2003 and 2019: Integration of field and satellite observations

Harmful algal blooms of the toxic dinoflagellate Karenia brevis occur almost annually on the West Florida Shelf (WFS) of the eastern Gulf of Mexico. To date, however, comprehensive assessments of K. brevis bloom spatial extent and temporal occurrence are lacking due to limitations in the two primary bloom monitoring techniques: microscopy evaluation of field-collected water samples and satellite remote sensing of ocean color. This is despite community efforts in expanding sampling coverage statewide and developing remote sensing algorithms to interpret color changes of surface waters. In this work, an approach is developed to combine the strengths of both techniques to estimate mean bloom occurrence frequency and bloom intensity as well as bloom extent at weekly, bi-weekly, monthly, and annual intervals between 2003 and 2019. Here, due to technical constraints on ocean color remote sensing, a bloom is defined as waters with K. brevis concentrations greater than 1.5 × 105 cells L−1. While microscopy examination of surface water samples provides K. brevis cell concentrations to help delineate bloom locations from Moderate Resolution Imaging Spectrometer on Aqua (MODIS/A) images, the imagery provides far more synoptic and frequent observations to make the bloom characterization statistically meaningful. Such derived bloom statistics often show bloom patterns that are not always known previously or at the time of the event, and in some years, they also differ from those determined from microscopic taxonomy data alone. For example, in terms of bloom size, two major bloom periods are observed in 2005 – 2007 and 2014 – 2018, respectively, when annual cumulative bloom size exceeded ∼50,000 km2. While preliminary in nature, the approach and results from this work may represent a first step to integrate water sample analysis and satellite remote sensing towards an improved characterization of K. brevis blooms on the WFS.

100 GSM paper as an SERS substrate for trace detection of pharmaceutical drugs in an aqueous medium

Surface-enhanced Raman spectroscopy (SERS) is a unique technique that allows us to detect samples in trace quantities. The spectral intensities of the characteristic Raman peaks of the analyte molecule are enhanced manifold in the presence of noble metal nanoparticles (NPs). The existence of NPs is necessary to couple the incident electromagnetic field with NPs through the localized surface plasmon resonance phenomenon, which primarily contributes to the enhancement of an SERS signal. The present work demonstrates the working of a paper-based SERS substrate to detect and quantify two pharmaceutical drugs—paracetamol and aspirin—in water. The proposed SERS substrate was obtained by drop-casting silver NPs over printing grade 100 grams per square meter (GSM) paper. 100 GSM denotes the class of paper where 100 grams of raw materials (cellulose) is used per square meter to manufacture the paper. The performance of the designed SERS substrate was initially evaluated with two Raman active samples—malachite green and rhodamine-6G. The applicability of the proposed SERS substrate was evaluated further through monitoring the Raman spectra of the two aforementioned pharmaceutical drugs in different field-collected water samples, thus establishing the reliability of the scheme in a real field environment.

Assessment of automated off-line solid-phase extraction LC-MS/MS to monitor EPA priority endocrine disruptors in tap water, surface water, and wastewater.

EPA method 539.1 recently introduced an expanded list of priority endocrine-disrupting compounds (EDCs), some of which were also included in the Unregulated Contaminant Monitoring Rule 3 (UCMR3). Though standardized methods are available for drinking water, analysis of steroid hormones and bisphenol A (BPA) at the ultra-trace level remains challenging. This study set out to evaluate the suitability of automated off-line solid-phase extraction (SPE) liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) for the determination of EPA-priority EDCs in environmental water matrixes (tap water, surface water, and wastewater influents and effluents). The target molecules included 14 steroid hormones (altrenogest, androstenedione, equilenin, equilin, α-estradiol, β-estradiol, estriol, estrone, ethinylestradiol, levonorgestrel, medroxyprogesterone, norethindrone, progesterone, testosterone) and BPA. Factors that may influence the analytical performance were assessed. This involved, for instance, testing combinations of SPE materials from different brands and protocol variations. Several materials presented absolute extraction efficiencies in acceptable ranges. Initial sample pH, nature of reconstitution medium, and mobile phase salt concentration were among the potential factors affecting analyte signal. Storage conditions (different preservative agents) possibly exerted the strongest influence, in agreement with the literature. Limits of detection were in the range of 0.03-0.5ng/L in drinking water, 0.1-0.5ng/L in surface water, and 0.16-1ng/L in wastewater. Method validation also involved testing linearity, accuracy, and precision in reagent water and matrix-matched extracted calibrants. The method was applied to field-collected water samples in Eastern Canada. Summed EDC concentrations remained low in tap water (<LOQ-0.92ng/L), while higher detection frequencies and contamination levels were reported in riverine surface waters (2.6-37ng/L) and municipal wastewaters (10-424ng/L).

A smartphone-based photometric and fluorescence sensing for accurate estimation of zinc ion in water

This paper demonstrates the development of a smartphone-based analytical system to determine zinc ion (Zn2+) concentration in water. The proposed system has been designed for simultaneous sensing in photometric and fluorescence mode on a single platform. Two inbuilt sensors of the phone, namely, the ambient light sensor (ALS) and the rear camera, have been utilized to develop the proposed sensing system. For photometric-based sensing, the ALS receives the transmitted modulated signal from the sample, while the rear camera records the fluorescence signal emitted from the sample at right angle to the direction of the excitation signal. The holder for the proposed sensing system has been fabricated in a 3D printer. A custom-designed android application has been developed to convert the proposed platform into a standalone tool. Using the designed sensor, Zn2+ ion concentration of field-collected water samples has been estimated successfully. Responses of the designed platform have been compared with the standard laboratory counterparts. The limit of detection and the percentage recovery of the proposed sensor are found to be 0.1 ppm and 103.10% respectively.

Endpoint PCR coupled with capillary electrophoresis (celPCR) provides sensitive and quantitative measures of environmental DNA in singleplex and multiplex reactions.

The use of sensitive methods is key for the detection of target taxa from trace amounts of environmental DNA (eDNA) in a sample. In this context, digital PCR (dPCR) enables direct quantification and is commonly perceived as more sensitive than endpoint PCR. However, endpoint PCR coupled with capillary electrophoresis (celPCR) potentially embodies a viable alternative as it quantitatively measures signal strength after PCR in Relative Fluorescence Units (RFU). Provided comparable levels of sensitivity are reached, celPCR permits the development of cost-efficient multiplex reactions, enabling the simultaneous detection of several target taxa. Here, we compared the sensitivity of singleplex and multiplex celPCR to dPCR for species-specific primer pairs amplifying mitochondrial DNA (COI) of fish species occurring in European freshwaters by analyzing dilution series of tissue extracts as well as field-collected water samples. Both singleplex and multiplex celPCR and dPCR displayed comparable sensitivity with reliable positive amplifications starting at two to 10 target DNA copies per μl extract. celPCR was suitable for quantifying target DNA and direct inference of copy numbers from RFU was possible after accounting for primer effects in linear mixed-effects models and calibration via dPCR. Furthermore, multiplex celPCR and dPCR were successfully used for the detection and quantification of fish-eDNA in field-collected water samples, confirming the results of the dilution series experiment and exemplifying the high sensitivity of the two approaches. The possibility of detection and quantification via multiplex celPCR is appealing for the cost-efficient screening of high sample numbers. The present results confirm the sensitivity of this approach thus enabling its application for future eDNA-based monitoring efforts.

Development of a quantitative PCR primers and probe for environmental DNA detection of Pacific herring Clupea pallasii

An eDNA assay for the detection of Pacific herring (Clupea pallasii) in water samples was developed using quantitative PCR (qPCR) technology. Species-specific primers and a minor groove binding (MGB) probe were designed based on the mitochondrial cytochrome b gene sequence. Upon conducting a cross-species test, the target species DNA was not only detected at low concentrations but also with high specificity. The assay was validated using field-collected water samples from aquatic environments known to be inhabited by Pacific herring and tested positive in samples from Pacific herring-inhabited sites. Our in silico, in vitro, and in situ results highlight the sensitivity of our proposed eDNA-based procedure for the detection of C. pallasii DNA, and could provide a non-invasive and non-destructive approach to detect this species and characterize its distribution in the Jinhaeman Bay, Korea.

The Effect of Activity, Energy Use, and Species Identity on Environmental DNA Shedding of Freshwater Fish

The quantitative measurement of environmental DNA (eDNA) from field-collected water samples is gaining importance for the monitoring of fish communities and populations. The interpretation of these signal strengths depends, among other factors, on the amount of target eDNA shed into the water. However, shedding rates are presumably associated with species-specific traits such as physiology and behavior. Although such differences between juvenile and adult fish have been previously detected, the general impact of movement and energy use in a resting state on eDNA release into the surrounding water remains hardly addressed. In an aquarium experiment, we compared eDNA shedding between seven fish species occurring in European freshwaters. The investigated salmonids, cyprinids, and sculpin exhibit distinct adaptions to microhabitats, diets, and either solitary or schooling behavior. The fish were housed in aquaria with constant water flow and their activity was measured by snapshots taken every 30 s. Water samples for eDNA analysis were taken every 3 h and energy use was determined in an intermittent flow respirometer. After controlling for the effect of fish mass, our results demonstrate a positive correlation between target eDNA quantities as measured with digital PCR, fish activity, and energy use, as well as species-specific differences. For cyprinids, the model based on data from individual fish was only partly transferable to groups, which showed lower activity and higher energy use. Our findings highlight the importance of fish physiology and behavior for the comparative interpretation of taxon-specific eDNA quantities. Species traits should therefore be incorporated into eDNA-based monitoring and conservation efforts.

Towards understanding the liver fluke transmission dynamics on farms: Detection of liver fluke transmitting snail and liver fluke-specific environmental DNA in water samples from an irrigated dairy farm in Southeast Australia

Livestock production around the world is impacted by liver fluke (Fasciola spp.) infection resulting in serious economic losses to the beef, dairy and sheep industries with significant losses of about $90 million per annum in Australia. Triclabendazole (TCBZ) is the most effective anthelmintic treatment available to control liver fluke infections; however, the widespread emergence of TCBZ resistance in livestock threatens liver fluke control. Alternative control measures to lower exposure of livestock to liver fluke infection would help to preserve the usefulness of current anthelmintic treatments. Environmental DNA (eDNA) based identification of liver fluke and the intermediate snail host in the water bodies is a robust method to assess the risk of liver fluke infection on farms. In this study, we used a multiplex quantitative PCR assay of water samples to detect and quantify eDNA of Fasciola hepatica (F. hepatica) and Austropeplea tomentosa (A. tomentosa), a crucial intermediate snail host for liver fluke transmission in South-east Australia. Water samples were collected from an irrigation channel for a period of 7 months in 2016 (February, March, May, September, October, November and December) at a dairy farm located at Maffra, Victoria, South-east Australia. Using an effective eDNA extraction method, the multiplex qPCR assay allows for the independent but simultaneous detection of eDNA released from liver fluke life stages and snails using specific primers and a probe targeting the ITS-2 region of the liver fluke and snail, respectively, with minimal inhibition from contaminants in field collected water samples. The sensitivity of this assay to detect eDNA of liver fluke and snails was observed to be 14 fg and 50 fg, respectively, in the presence of field collected water samples. Differential levels of liver fluke and snail specific eDNA in water were observed at the time points analysed in this study. The successful detection of eDNA specific to liver fluke and snails from the field collected water samples provides a precedent for the use of this method as a monitoring tool to determine the prevalence of liver fluke and liver fluke-transmitting snails in irrigation regions. Further, this method has the enormous potential to allow an assessment of the liver fluke transmission zones on farms and to inform the application of effective control strategies.

A framework for the analysis of polar anticancer drugs in wastewater: On-line extraction coupled to HILIC or reverse phase LC-MS/MS

With the consumption of chemotherapy agents, residues of anticancer drugs may be increasingly found in hospital and municipal wastewaters. Quantification of these highly polar micropollutants remains challenging due to poor chromatographic retention on typical reversed phases. This study investigated different solid-phase extraction (SPE) materials for automated on-line preconcentration of complex matrices (hospital and municipal wastewaters) and various chromatographic column options. A hyper crosslinked hydroxylated polystyrene-divinylbenzene copolymer SPE sorbent coupled on-line with hydrophilic interaction liquid chromatography tandem mass spectrometry (HILIC-MS/MS) yielded suitable limits of detection (LOD: 1–2 ng L−1) for 5-fluorouracil (5-FU) and 2’,2’-difluorodeoxyuridine (dFdU). Optimization of chromatographic conditions led to a single LC-MS/MS method for the analysis of other cytostatic drugs including cytarabine (CYT), gemcitabine (GEM), methotrexate (MTX), ifosfamide (IFO), cyclophosphamide (CYC) and capecitabine (CAP). The filter membrane for sample pre-treatment, HPLC mobile phase additives, and on-line SPE loading parameters were also investigated. The methods were validated in wastewater matrix with suitable determination coefficients (R2 range: 0.9982–0.9999), LODs (0.5–5 ng L−1), accuracy (78–111%), intraday precision (2.6–12%), and interday precision (2.1–13%). The occurrence of cytostatic drugs was examined in field-collected water samples from hospital effluents and municipal wastewater treatment plants (WWTP) in Canada. CAP (3.7–64 ng L−1), dFdU (6.1–300 ng L−1), and MTX (1.8–68 ng L−1) were frequently detected across both matrix types, while IFO was detected in hospital wastewater (23–140 ng L−1) but not in municipal WWTPs.

Estimation of trace-mercury concentration in water using a smartphone

This paper demonstrates a smartphone-platform sensing system for rapid and accurate estimation of mercury (Hg2+) concentration in water. The principle of the proposed sensor is based on the detection of the fluorescence signal intensity emitted from rhodamine6G (R6G) in presence of Hg2+ ion in the solution. With the increase of Hg2+ ion concentration in potassium-iodide (KI) buffered R6G solution, the fluorescence emission is gradually quenched and the designed smartphone sensor can easily detect this variation. A compact optical setup has been designed using a 3D printer that houses all the required optical components. The compact setup can be attached to the rear camera of the smartphone. The performance of the sensor has been evaluated in presence of other interfering elements in the sample. Furthermore, the sensing performance of the sensor has been successfully demonstrated through measuring Hg2+ ion concentration from different field-collected water samples.

Improving the yield of environmental DNA from filtered aquatic samples

Analysis of environmental DNA (eDNA) through non-invasive sampling continues to gain popularity in the surveillance of organisms. Methodological improvement to ensure maximum DNA recovery from the samples would benefit future studies. We investigated the effects of DNA extraction methods and filter preservation methods on eDNA yield by analyzing field-collected water samples for eDNA of the Eastern Hellbender (Cryptobranchus a. alleganiensis). We tested whether the use of bead beating during DNA extraction, which likely facilitates removal of cells trapped on filters, would increase eDNA yield. We also examined whether preservation of filters in ethanol or storage at − 20 °C before extraction would yield more eDNA. Bead beating and preservation at − 20 °C significantly increased the estimated amount of eDNA.

Burrowing behavior of Chironomus yoshimatsui larvae as an indicator of freshwater quality

A new behavioral endpoint in ecotoxicity testing, burrowing behavior of Chironomus yoshimatsui larvae that survived pre-exposure to 0, 1, 5, and 10mg/L of cadmium for 96h was evaluated in a system composed of clean reconstituted water and sand for 5h, at 30min intervals. The effective time required for 50% of the introduced larvae to burrow (ET50), the proportion of the maximum burrowing rate reached during a 5h period (BR5h), and the area under the curve at 5h (AUC5h) were calculated based on the fitted relationship between burrowing rate and elapsed time. These effect parameters were chosen because they take into account either the burrowing speed of the larvae (ET50), or the proportion of the maximum burrowing rate reached during a 5h period (BR5h), or both (AUC5h). We found that higher cadmium concentrations resulted in longer ET50 and lower AUC5h values. Additionally, field water samples were collected from streams near residential, natural, agricultural, and industrial areas in Ansan City, Korea in 2014 and 2015, and were used to validate the proposed burrowing test method. The results of the burrowing tests with field collected water samples also confirmed the sensitivity of burrowing activity as an ecotoxicity endpoint, indicated by the large differences among the ET50, BR5h, and AUC5h across the sampling sites and dates with industrial sites strongly affecting burrowing behavior. This study clearly showed that the proposed burrowing test could provide information that would not be detected with the existing acute toxicity tests, within a relatively short time, and can therefore be used as a complement to existing chemical analyses and acute toxicity tests.

Water Hardness Removal by Coconut Shell Activated Carbon

The present study reports the water softening by adsorption of hardness ions onto Coconut Shell Activated Carbons (CSAC). Characterization of CSAC was identified by FT-IR and SEM techniques. Batch experiments were carried out to determine the effect of various adsorbent factors such as adsorbent dose, initial pH, contact time, and temperature, on the adsorption process using synthetic and field collected water samples. Removal efficiency at nearly neutral pH of 6.3 for both synthetic and field collected water samples were 60% and 55% respectively. Temperature study (303 K-333 K) shows that the softening process in synthetic and field hard water is endothermic as removal efficiency was increasing from 40% and 29% at 303 K to 47% and 38% at 333 K respectively. Removal efficiency increases with the increase in contact time and adsorbent dose until 15 hours and 0.24g/cm3 respectively, for both field and synthetic hard water, which was considered to be maximum. Equilibrium isotherms have been analyzed using Langmuir and Freundlich isotherm models, and both Freundlich and Langmuir isotherm models fit to explain the adsorption behavior of hardness ions onto CSAC.

Method development for the analysis of organophosphate and pyrethroid insecticides at low parts per trillion levels in water

In the current study, organophosphate and pyrethroid insecticides including diazinon, chlorpyrifos, bifenthrin, fenpropathrin, permethrin, λ-cyhalothrin, cyfluthrin, cypermethrin, esfenvalerate and deltamethrin were analyzed in laboratory and field-collected water samples. Water samples were extracted and analyzed by gas chromatography/electron capture detector (GC/ECD) and gas chromatography/nitrogen–phosphorous detector (GC/NPD). Comparison of results from liquid–liquid extraction and subsequent normal phase solid-phase extraction cleanup (LLE–NPSPE), and reversed phase solid-phase extraction (RPSPE) showed that LLE–NPSPE was the better choice to extract trace amounts of pesticides from water. Pesticide recoveries from four spiked water samples using LLE–NPSPE ranged from 63.2 to 148.8% at four spiking concentrations. Method detection limits were 0.72–1.69 ng/L using four different water sources. The stability of the target pesticides in lake water was investigated at 4 °C for 1 h, 1 d, 4 d, and 7 d under three conditions: (1) water samples only; (2) with 20 mL hexane used as a keeper solvent; and (3) with acidification to pH 2 with HCl. Results showed that water storage without treatment resulted in slow degradation of some pesticides with storage time, storage using water acidification led to significant degradation and loss of diazinon and chlorpyrifos, while water storage with hexane as a keeper solvent showed good stability for all of the target pesticides over the 7 d storage period.

Genotoxicity in native fish associated with agricultural runoff events

The primary objective of the present study was to test whether agricultural chemical runoff was associated with in-stream genotoxicity in native fish. Using Sacramento sucker (Catostomus occidentalis), we combined field-caging experiments in an agriculturally dominated watershed with controlled laboratory exposures to field-collected water samples, and we coupled genotoxicity biomarker measurements in fish with bacterial mutagenicity analysis of water samples. We selected DNA strand breakage as a genotoxicity biomarker and Ames Salmonella mutagenicity tests as a second, supporting indicator of genotoxicity. Data from experiments conducted during rainfall runoff events following winter application of pesticides in 2000 and 2001 indicated that DNA strand breaks were significantly elevated in fish exposed to San Joaquin River (CA, USA) water (38.8, 28.4, and 53.6% DNA strand breakage in year 2000 field, year 2000 lab, and year 2001 field exposures, respectively) compared with a nearby reference site (15.4, 8.7, and 12.6% DNA strand breakage in year 2000 field, year 2000 lab, and year 2001 field exposures, respectively). Time-course measurements in field experiments supported a linkage between induction of DNA strand breakage and the timing of agricultural runoff. San Joaquin River water also caused significant reversion mutation in two Ames Salmonella tester strains. Salmonella mutagenicity corroborated in-stream effects, further strengthening a causal relationship between runoff events and genotoxicity. Potentially responsible agents are discussed in the context of timing of runoff events in the field, concordance between laboratory and field exposures, pesticide application patterns in the drainage, and analytical chemistry data.

Field evaluation of plaster-based temephos pellets for residual control of midge larvae (Diptera: Chironomidae) in establishing rice crops

A pelletised formulation of temephos (5% a.i.) was evaluated as a potential control agent for chironomid midge larvae in establishing rice crops. Four application rates between 0.03 and 0.53 mg a.i./L (42-732 g a.i./ha) were applied to 80 m2 experimental rice bays immediately after flooding. Water samples and soil core samples were taken at regular intervals until 29 days post-treatment. Larvae were extracted from core samples using magnesium sulfate (MgSO4) flotation, whilst laboratory-reared fourth instar Chironomus tepperi Skuse larvae were used in bioassays with field-collected water samples to determine pesticide activity in the water column. All treatments significantly suppressed C. tepperi-type larvae in the field for at least 13 days. Some suppression of non-C. tepperi-type larvae was obtained at 0.27 mg a.i./L, whilst at 0.53 mg a.i./L all chironomids were reduced to negligible levels for the full period of the trial. In bioassays, significant levels of water column toxicity to fourth instar C. tepperi larvae were only recorded for 2 days after treatment at the highest application rate. Our results indicate that plaster-based temephos pellets have the potential to provide effective, single application control of chironomid larvae in establishing rice crops without the risk of spray drift inherent in the aerial application of liquid insecticides.

Estimating Water Salinity with Geophysical Earth Resistivity Equipment

AbstractA procedure is described for estimating salinity of water samples in the field using a geophysical earth resistivity meter and four‐electrode conductivity cell. Using field collected water samples, a linear relationship of Y = 1.02(X) + 0.12, r = 0.996, was obtained between EC25 values determined using a commercial laboratory bridge and cell (Y), and those determined using an earth resistivity meter and an easily fabricated, four‐electrode conductivity cell (X).