Levels Of Toxic Substances Research Articles

A BIM-Based Approach for Assessing Occupational Health Risks in a Building Construction Project

Construction work sites and the surrounding built environments are notable contributors to atmosphere dust particulate matter (PM) emissions. PM produced in construction processes contain a range of chemically hazardous substances, posing significant health risks (HR) to individuals. As such, the evaluation of occupational HR in construction has become a focal point of interest internationally. Initiated in the early 2000s, there has been a growing demand within the construction research community for the creation of a unified PM database that encapsulates a wide array of construction activities. Previous studies have endeavored to establish a PM database for various construction contexts, yet they have fallen short in thoroughly addressing the diversity of construction materials and the levels of toxic substances (TS) within the PM. This research introduced a comprehensive PM and TS dataset and conducted a case study to measure the HR associated with diverse construction processes. This was accomplished by implementing a semi-automated Building Information Modeling (BIM) version 2020-based plugin, which streamlines the assessment of occupational HR in construction projects. This system provides construction supervisors with a tool to visually assess the HR of daily operations, thereby facilitating the adoption of preemptive measures to protect the health of construction workers.

Physicochemical properties, total hydrocarbon content, and trace metals of water and sediments from major River Estuaries within the Niger Delta Region of Nigeria

Water and sediment samples from Cross River, Imo River, and Qua Iboe River Estuaries were collected and treated using standard analytical procedures. The samples were analyzed for their physicochemical properties, total hydrocarbon content (THC), and trace metals. Results obtained revealed that, the mean levels of total suspended solids (TSS), total dissolved solids (TDS), turbidity, colour, biochemical oxygen demand (BOD), THC, cadmium (Cd), iron (Fe), nickel (Ni), lead (Pb), and zinc (Zn) in water were higher than their acceptable limits in Nigeria. Whereas, the mean levels water pH, electrical conductivity (EC), dissolved oxygen (DO), nitrate, sulphate, phosphate, and copper (Cu) were within their acceptable limits. The results obtained also revealed that, the mean levels of nitrate, THC, and Fe in sediments were higher than their recommended limits. While the levels of pH, EC, sulphate, phosphate, Cd, Cu, Ni, Pb, and Zn in sediments were within their recommended limits. This study indicated that the anthropogenic activities by oil and oil-related companies within the Niger Delta Region of Nigeria may have contributed significantly to the high level of toxic substances in the water channels within the zone. The results obtained revealed that, the direct or indirect exposure to untreated water from the studied water channels may result in serious health challenges. Hence, the environment should be closely monitored to forestall a devastating situation in the region.

Physical-chemical characteristics and ecological cleanliness of wild forest berries in the Vologda Region

In recent years, the demand for forest food and medicine products has increased, as it is a source of vitamins, minerals and biologically active substances. In addition, they are more environmentally favorable food products and are not processed with chemicals during the growth period. High nutritional value or useful medicinal properties are reduced to zero when the level of toxic substances in them exceeds the maximum permissible norms. Research on the ecological purity of wild plants is an urgent issue. The object of the study is wild-growing berries growing in the Vologda Region. The study used generally accepted methods in assessing the food safety of food products. As a result, it was established that the Vologda Region has a significant resource potential of wild berries. Procurement can be carried out on an area of 110510 thousand km2, and the estimated annual amount of resource withdrawal may be 40591.1 tons. The quality of berry raw material exceeds established standards. When assessing environmental cleanliness, it was found that wild forest berries of the Vologda Region contain less cesium-137 and nitrates than the maximum permissible levels of hazardous concentrations. This fact indicates the possibility of using berries in food production, including baby food.

Recycling potential of powdered cigarette waste in the development of ceramic materials

The final disposal of hazardous waste, such as cigarette waste, cannot be the same as conventional urban solid waste because it has considerable levels of toxic substances. In this context, this work presents a methodology for the application of cigarette waste in clay mixtures at incorporation ratios of 0%, 2.5%, 5%, 7.5% and 10%. 50 × 6 mm cylindrical specimens were tested in compression, water absorption and shrinkage after firing at 900 °C. Even with a reduction in the evaluated parameters, it was proved that the use of up to 5% of cigarette waste is technically feasible. Gas chromatogram, dilatometry, mercury intrusion porosimetry and scanning electron microscopy tests were also performed. These tests helped to prove that the loss of mechanical properties occurred due to the increase of the porosity of the red ceramic artifacts with the incorporation of cigarette waste, as a result of the combustion of the organic matter present in the waste. However, this combustion is also beneficial because it increases energy efficiency during the burning of ceramic products. The feasibility of using up to 5% cigarette waste in ceramic materials has been proven, provided that the waste is dispersed and homogenized within the clay in the production of the raw materials.

Radiological Assessment of Reservoirs in Volyn Region that is Under Radioactive Contamination

Purpose. To determine the content of radionuclides 137Сs, 90Sr and heavy metals in water bodies within the boundaries of settlements of Kamyn-Kashirsky, Lyubeshivsky and Manevychi administrative districts of Volyn region. Methods. During the expedition and laboratory work, standard methods of sampling, preparation and measurement of samples were used according to the current methods of radiochemical, radiospectrometric, ichthyological, hydrochemical, statistical analyses, etc. The determination of the total content of heavy metals was performed in laboratory conditions by conventional methods. Results. The research is based on its own analyses, as well as the stock materials of the Scientific Information Center for Water Management and Ecological Monitoring and Optimization of Water Use. Features of 137Сs, 90Sr radionuclides distribution in reservoirs (water, sediments, fish, birds) within the zone of radioactive contamination in Volyn Region are considered. The maximum concentrationі of 137Сs, 90Sr in the studied area were determined. The anthropogenic impact and excess of the maximum permissible concentrations and maximum permissible levels of toxic substances in the ecosystem links of certain water bodies of the partially contaminated region are identified. Conclusions. As a result of the study on the level of concentrations of 137Сs and 90Sr and heavy metals in water (within the boundaries of settlements) of the investigated area, it was found that reservoirs in village of Prylisne, village of Velyka Osnytsya, village of Cherevakha in Manevitsky District, village of Nuyno in Kamin-Kashirsky District and the village of Vetly in Lyubeshiv Administrative Distict are affected by the highest concentrations of 137Сs and 90Sr. The significant content of heavy metal salts is recorded in the reservoirs, namely in the village of Serhiv – lead, village of Prylisne in Manevytskyi District– zinc, cadmium; in the village Berezna Volia in Lyubeshiv District – copper; in the village of Nuyno in Kamin-Kashirsky District – lead.

A Multiscale Spatially Varying Coefficient Model for Regional Analysis of Topsoil Geochemistry

A motivating example for this paper is to study a topsoil geochemical process across a large region. In regional environmental health studies, ambient levels of toxic substances in topsoil are commonly used as surrogates for personal exposure to toxic substances. However, toxicity levels in topsoil are usually sparsely measured at a limited number of point locations. Consequently, topsoil measurements only provide highly localized regional information and cannot be representative of the surrounding area. Instead, it is standard practice to use point-referenced measurements of stream sediments, because they are widely available across a region and are correlated with topsoil measurements at nearby locations. For more effective regional modeling of topsoil geochemistry, we develop a spatially varying coefficient model that integrates point-level topsoil and point-referenced area-level stream sediment data. The proposed model incorporates two spatial characteristics: the local spatial autocorrelation in the latent topsoil process and the spatially varying relationship between the latent topsoil and stream sediment processes. The former is modeled indirectly via a conditional autoregressive model for the stream sediment process, and the latter is modeled by spatially varying coefficients that follow a multivariate Gaussian process. We apply the proposed model to a real dataset of arsenic concentration and demonstrate better performance than competing models.

Morphological and molecular response of small intestine to lactulose and hydrogen-rich water in female piglets fed Fusarium mycotoxins contaminated diet

BackgroundFollowing the intake of Fusarium mycotoxin-contaminated feed, small intestines may be exposed to high levels of toxic substances that can potentially damage intestinal functions in livestock. It is well known that Fusarium mycotoxins will lead a breakdown of the normally impeccable epithelial barrier, resulting in the development of a “leaky” gut. H2 administration with different methods has been proved definitely potentials to prevent serious intestinal diseases. The goal of this study is to investigate the roles of lactulose (LAC) and hydrogen-rich water (HRW) in preventing intestinal dysfunction in piglets fed Fusarium mycotoxin-contaminated feed.MethodsA total of 24 female piglets were evenly assigned to 4 groups: negative control (NC) group, mycotoxin-contaminated (MC) feed group, MC feed with LAC treatment (MC + LAC), and MC feed with HRW treatment (MC + HRW), respectively. Piglets in the NC group were fed uncontaminated control diet, while remaining piglets were fed Fusarium mycotoxin-contaminated diet. For the NC and MC groups, 10 mL/kg body weight (BW) of hydrogen-free water (HFW) was orally administrated to piglets twice daily; while in the MC + LAC and MC + HRW groups, piglets were treated with the same dose of LAC solution (500 mg/kg BW) and HRW twice daily, respectively. On d 25, serum was collected and used for biochemical analysis. Intestinal tissues were sampled for morphological examination as well as relative genes and protein expression analysis.ResultsOur data showed that Fusarium mycotoxins induced higher serum diamine oxidase (DAO) activities (P < 0.05), D-lactic acid levels (P < 0.01), and endotoxin status (P < 0.01), lower villus height (P < 0.01) and ratio of villus height to crypt depth (P < 0.05) in small intestine, greater apoptosis index and higher mRNA expression related to tight junctions (P < 0.05). In addition, the distribution and down-regulation of claudin-3 (CLDN3) protein in the small intestinal was also observed. As expected, oral administrations of HRW and LAC were found to remarkably provide beneficial effects against Fusarium mycotoxin-induced apoptosis and intestinal leaking. Moreover, either HRW or LAC treatments were also revealed to prevent abnormal intestinal morphological changes, disintegrate tight junctions, and restore the expression and distribution of CLDN3 protein in the small intestinal mucosal layer in female piglets that were fed Fusarium mycotoxins contaminated diet.ConclusionsOur data suggest that orally administrations of HRW and LAC result in less Fusarium mycotoxin-induced apoptosis and leak in the small intestine. Either HRW or LAC treatments could prevent the abnormal changes of intestinal morphology and molecular response of tight junctions as well as restore the distribution and expression of CLDN3 protein of small intestinal mucosa layer in female piglets that were fed Fusarium mycotoxins contaminated diet.

First Report of Tumor-Like Anomalies on the Copepods and their Seasonality from the Obhur Creek, Jeddah Coast, Central Red Sea

Monthly abundance of the subclass Copepoda was analyzed from the zooplankton samples collected at Obhur Creek, Jeddah, Saudi Arabia during December-2011 till December-2012. Zooplankton samples were collected through surface horizontal tows by a modified WP2 net (via. mouth diameter 50 cm, length 180 cm, 150 μm mesh size). Order Calanoida dominated the abundance with mean annual average of 75.29%. We observed abnormal protuberances on copepods, known as tumour-like anomalies (TLAs). Calanoida showed more frequent and prominent TLAs on its dorsal surface with highest mean percentage occurring during Jun. 2012 (1.64%). The percentage prevalence of TLAs on the Copepoda was highest during Jun. 2012 (1.36%) and least during Nov. 2012 (0.03%). It is suggested that these TLAs might be caused due to the presence of potentially high levels of toxic substances, which weakens the exoskeleton and thereby making them more susceptible to infections or due to wounds from parasites or might be related to the occurrence of symbiotic tantulocarids or might be due to the radiation stress as a control measure. Whatever the reason, these TLAs have become a serious emerging threat to the aquatic food web. Our investigation is the first of its kind in the coastal waters of the Saudi Red Sea, which needs further investigations in order to elucidate the possible reasons for these abnormalities.

Water-pipe smoke condensate increases the internalization of Mycobacterium Bovis of type II alveolar epithelial cells (A549)

BackgroundTuberculosis (TB) is a major global health problem, and there is an association between tobacco smoke and TB. Water pipe smoking has become an increasing problem not only in Middle Eastern countries but also globally because users consider it as safer than cigarettes. The presence of high levels of toxic substances in water-pipe smoke may be a predisposing factor that enhances the incidence of pulmonary disorders. For example, uncontrolled macropinocytosis in alveolar epithelial cells following exposure to water-pipe smoke may predispose subjects to pulmonary infection. Here, we studied the effects of water-pipe condense (WPC) on the internalization of Mycobacterium Bovis BCG by macropinocytosis in the alveolar epithelial cell line A549.MethodsA549 cells were exposed to WPC (4 mg/ml) for 24, 48, 72 and 96 h. Cell viability was studied using the methyl thiazolyldipenyl-tetrazolium bromide (MTT) reduction assay and proliferation by bromodeoxyUridine (BrdU) incorporation. Cells were exposed to FITC-Dextran (1 mg/ml) (as a control) and FITC-BCG (MOI = 10) for 20 min at 37 °C before cells were collected and the uptake of BCG-FITC determined by flow cytometry. Similar experiments were performed at 4 °C as a control. The Rho-associated protein kinase (ROCK) inhibitor Y-27632 (1 μM) was used to assess the mechanism by which WPC enhanced BCG uptake.ResultsWPC (4 mg/ml) increased the uptake of BCG-FITC after 72 (1.3 ± 0.1 fold, p < 0.05) and 96 (1.4 ± 0.05 fold, p < 0.05) hours. No effect on BCG-FITC uptake was observed at 24 or 48 h. WPC also significantly increased the uptake of FITC-Dextran (2.9 ± 0.3 fold, p < 0.05) after 24 h. WPC significantly decreased cell viability after 24 (84 ± 2%, p < 0.05), 48 (78±, 3%, p < 0.05), 72 (64 ± 2%, p < 0.05) and 96 h (45 ± 2%, p < 0.05). Y-27632 completely attenuated the increased uptake of BCG by WPC. Cell proliferation showed a decreasing trend in a time-dependent manner with WPC exposure.ConclusionWPC exposure increased epithelial cell endocytosis activity and death as well as enhancing their capacity for macropinocytosis. Our in vitro data indicates possible harmful effects of WPC on the ability of lung epithelial cells to phagocytose mycobacterium.

Determination of the priority substances regulated by 2000/60/EC and 2008/105/EC Directives in the surface waters supplying water treatment plants of Athens, Greece

ABSTRACTAn investigation into the occurrence of priority substances regulated by 2000/60/EC Water Framework Directive and 2008/105/EC Directive was conducted for a period of one year in the surface water sources supplying the water treatment plants (WTPs) of Athens and in the raw water of WTPs. Samples from four reservoirs and four water treatment plants of Athens were taken seasonally. The substances are divided into seven specific groups, including eight volatile organic compounds (VOCs), diethylhexylphthalate, four organochlorine pesticides (OCPs), three organophosphorus/organonitrogen pesticides (OPPs/ONPs), four triazines and phenylurea herbicides, pentachlorophenol, and four metals. The aforementioned substances belong to different chemical categories, and different analytical methods were performed for their determination. The results showed that the surface waters that feed the WTPs of Athens are not burdened with significant levels of toxic substances identified as European Union (EU) priority substances. Atrazine, hexachlorocyclohexane, endosulfan, trifluralin, anthracene and 4-nonylphenol were occasionally observed at very low concentrations. Their presence in a limited number of cases could be attributed to waste disposal, agricultural activities, and to a limited industrial activity in the area nearby the water bodies.

Suitability of Printing Materials for Heat-Induced Inkless Eco-Printing

Pyrolysis volatiles and the environmental impact of printing paper, newspaper, and silk were investigated to identify suitable materials for heat-induced eco-printing (HIEP) using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Furthermore, the printing effects of simulated HIEP and the material microstructures were studied using scanning electron microscopy (SEM). The results indicated that the toxicity of pyrolysis volatiles is highest for newspaper, followed by silk and then printing paper, whereas environmental friendliness follows the opposite trend. A high concentration of lignin, the basic structural element of which is phenyl propane, and the presence of halogens in the newspaper led to the generation of more toxic substances during the pyrolysis process. The benzene compounds and heterocyclic compounds in silk also produced high levels of toxic substances. Based on these findings and the higher color permeability of newspaper, printing paper was the most suitable material for HIEP and newspaper was the least suitable. Additionally, silk may still be used in HIEP in small amounts for the production of art, name cards, and clothing tags.

Burning solid fuel in the low-temperature fluidized bed with determining toxic emissions

In conditions of the unstable economic situation and constant rise in prices of natural gas for utility enterprises in Ukraine, transition to local low-quality fuels is topical. A promising method of burning low-quality high-ash and low-calorie fuels with low level of toxic substances is burning in the low-temperature fluidized bed. Technology for burning low-quality fuel in the low-temperature fluidized bed furnace is environmentally attractive and can allow enterprises to switch to cheaper local solid fuels. However, burning is a complex technological process, which requires additional researches. Burning in the low-temperature fluidized bed differs from the traditional burning of fuel by increased energy efficiency of the fuel use, low pollutant emissions. The results of the experiments, conducted on the developed laboratory setup, on burning various low-quality solid fuels such as brown coal, peat, pellets, coal of rank (D), and anthracite culm in the low-temperature fluidized bed are given in the work. A number of experiments, which allowed to obtain the ranges of burning the above solid fuels in the fluidized bed is provided, the critical temperatures, at which it is necessary to add more fuel to the fluidized bed furnace are defined in the paper. Also, toxic emissions when burning these solid fuels in the fluidized bed are determined. The obtained results can be used to configure automatic equipment, regulating the operation of fluidized bed furnaces, working on low-quality fuels, reconstruct and modernize the existing boilers for their transition to the low-quality fuels with reduced pollutant emissions.

Detection of Carbamates and Organophosphorus Pesticides and Residues in Selected Vegetables in Northern Philippines

Acute pesticide poisoning is a serious public health problem in developing countries like the Philippines. Pesticides like organophosphates (OP) and carbamates are the most widely used pesticides in the world. The presence of these pesticides and their residues from two vegetable provincial producers: La Trinidad, Benguet and Bambang, Nueva Vizcaya in Northern Philippines were determined using the Colorimetric Spot Technique. The source (Factor A) and the type (Factor B ) of vegetables were examined using the Randomized Complete Block Design (RCBD) in Factorial with three replications to allocate treatments. Results showed that the source and type of vegetables were not statistically significant on the amount of pesticide residue. Source and vegetable combination interaction had no statistical significance on the amount of pesticide residue. However, cabbage (T1) was found to have the highest amount of organophosphate pesticide residue followed by Chinese pechay (T2) and cauliflower (T3). In terms of location or vegetable source, both Benguet (S1) and Nueva Vizcaya (S2 ) showed the presence of pesticide residue. String beans, Baguio Beans and tomatoes registered positive with the Carbamate Detection Kit. The study concludes that none of the treatments analyzed exceeds the safe level of toxic substances as to source and type. Keywords - carbamates, organophosphates, colorimetric spot technique, cruciferae, pesticide , residue

황사의 대기환경영향

ACE-Asia (Asian Pacific Regional Aerosol Characterization Experiment) in spring 2001 was a turning point to trigger international research interest on Asian dust (AD). This basically arose from the lack of research on AD, the important natural phenomenon to characterize the Northeast Asia. In contrast, health risk related to AD has been the primary concern in Korea. Although due in part to severe AD events of 2001~2002, research and mitigation measures on AD in Korea are typically based on the assumption that AD events are increasing in frequency and severity. However, contrary to the trend in Korea, the number of AD days and emission amounts of AD in China have decreased since 1980s. This paper reviews the impacts of AD on ambient air quality and variations in toxic substances during the AD event, reflecting the concern in Korea. While a great amount of dust particles flow into Korea during the AD event, a considerable amount of dust particles are locally generated as well. Since dust particles are mixed with toxic substances as they pass over polluted areas, the levels of toxic substances become lower in dust particles that do not pass over polluted areas. Broadening the research scope on AD is warranted to understand the AD as an important natural phenomenon, irrespective of its associated health risk.

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in seawater of the Southern Baltic Sea

Due to the low concentrations of persistent organic pollutants (POPs) in seawater, a special method of analysis is needed. The aim of this work was to prepare the detailed procedure for the determination of POPs in seawater and establish the level of pollution by selected POPs (seven PCBs, DDT and its metabolites, HCH isomers, HCB) of the surface and near bottom water from the Baltic Sea. The levels of toxic substances were analysed using capillary gas chromatography (GC). The average values of SHCH, HCB, SDDT and Σ7PCBs in the surface water were 0.35 (±0.13) ng dm−3, 0.06 (±0.02) ng dm−3, 0.14 (±0.05) ng dm−3 and 0.98 (±0.44) ng dm−3, respectively. The average concentrations of ΣHCH, HCB, ΣDDT and Σ7PCBs analysed near bottom water were 0.44 (±0.16) ng dm−3, 0.09 (±0.02) ng dm−3, 0.17 (±0.08) ng dm−3 and 0.95 (±0.57) ng dm−3.

Environmental Situation in the Lower Dnipro River Basin

Abstract The paper summarizes Ukrainian findings and conclusions of the first Ukrainian-Canadian field study on the state of the environment in the Lower Dnipro River Basin. Three major issues were identified during the field study: accelerated eutrophication from municipal and agro-industrial discharges, industrial pollution, and radionucleide contamination of reservoir sediments. The Dnipropetrovsk-Zaporizhzhia-Kryviy Rih triangle has been recognized as an area which has been greatly affected by pollutants originating from many activities, including heavy industry, oil refining, metallurgy, petrochemistry, mining and power generation. The results of biological assays demonstrated that the Lower Dnipro River is endangered by toxic pollution originating from poorly treated or untreated effluent discharges. Of 58 industrial wastewater samples, taken at 31 outlets of the Dnripo and its tributaries, 69% contained various levels of toxic substances. Various degrees of toxicity were detected in 97% of 53 of the wastewater samples, taken at 37 sites. As a result, the majority of the tributaries sampled were of poor water quality and exceeded the statutory pollution standards. The diversity of phyto- and zooplankton was found to be severely reduced as was the native fish population in the Dnipro reservoirs. The maximum Cs-137 concentrations in bottom sediments of the Dnipro reservoirs varied from 31 to 520 Bq/kg, with the highest levels occurring in the reservoir closest to Chernobyl. The Ukranian government has identified the Lower Dnipro Basin as a top priority area for a strategic remedial action plan.

Chemical evaluation of the nutritive value and changes in ascorbic acid content during storage of the fruit of ‘bitter kola’ ( Garcinia kola)

The nutritive value of the pericarp and mesocarp of Garcinia kola was evaluated using chemical analysis. The pericarp was richer than the mesocarp in crude fibre and in macro elements other than phosphorus and nitrogen. The mesocarp was richer than the pericarp in protein, crude lipid and ascorbic acid. Levels of toxic substances in both the mesocarp and pericarp were low, but the juice was highly acidic. The effects of traditional and refrigerated storage on ascorbic acid content were monitored. This study revealed that it was better to store the fruits at 10 °C, while the seeds could be better stored by the traditional method in layers of red clay soil (Ikoneto).

Analysis of fume emission from ultrasonic removal of methyl methacrylate cement in revision hip surgery

Fumes emitted from the ultrasonic instrument while removing polymethyl methacrylate cement were analyzed in three separate phases: phase 1, cement removal from bovine femur in the laboratory; phase 2, methyl methacrylate fumes collected at primary cemented total knee arthroplasty; and phase 3, fumes collected at revision hip surgery. These fumes were collected via personal sampling pumps worn by operating room personnel to determine personal levels of exposure. In phase 1 peak levels of methyl methacrylate and butyl methacrylate were obtained. Phase 2 revealed the highest levels of methyl methacrylate to be only 1 part per million or less (well below the National Institute for Occupational Safety and Health recommended exposure limit of 100 parts per million), and in phase 3 there were no detectable levels of toxic substances. Therefore, we feel that the fumes emitted from the use of ultrasound in revision total hip arthroplasty are safe.

An evaluation of the potential for toxics exposure in the Great Lakes region using STORET data

It has been suggested that residents of the Great Lakes region are at a greater risk of exposure to toxic substances than any other subset of the United States population. This project tested the potential for exposure to toxics by using the levels of toxic substances in fish tissue and sediment as surrogates for human exposure. Data were retrieved from the EPA's STORET database and sorted by USGS water resource regions. The results indicate that the overall potential for exposure to toxics in the Great Lakes region is not higher than other geographic regions.

Some comments on analysis techniques for censored water quality data

When investigating trace substances in ambient water, a proportion of water sample concentrations is usually below limits of detection. In medical and industrial reliability studies, comparisons are often made of time to event data which includes right censored observations indicating only that an observation is greater than a specified value. In this paper consideration is given to the application of non-parametric procedures, widely used in the analysis of time to event data, to water quality data which is left censored.A non-parametric estimate of the cumulative distribution function for left censored water quality data can be generated quite easily. For the comparison of levels of trace substances it is necessary to combine an unconditional likelihood for the proportion of observations below a detection limit with a partial likelihood for the portion of the distribution above the detection limit in order to make use of regression methodology. The details of this are outlined and an example is given which compares levels of toxic substances at the head and mouth of the Niagara river.When comparisons are based on matched pair data, further modifications are necessary. A development paralleling that for time to event data is given. Consideration is also given to model extensions which allow for a dependence between observations at the same location over a period of time.The presentation is introductory and designed to illustrate the potential of some available methodology for use in the analysis of water quality data.