Effect of cigarette smoking on residential NO2 levels

Two studies evaluating the levels and sources of nitrogen dioxide in approximately 90 employee homes in the Richmond area with continuous sampling during the weeks of August 5, 1980, and February 9, 1981, were performed using samplers in the living room, bedroom, kitchen, and outdoors. Additional data were collected concerning appliance usage, heating/cooling plant, ventilation and cigarette smoking. Results were analyzed using BMDP routines. The largest contributor to NO₂ concentration was found to be gas-fired kitchen appliances. The mean kitchen level for homes with gas appliances during the winter study was 188 μg/m³. Excluding participants with gas kitchens, incremental influence due to cigarette smoking was detected. The 7-day, 3-room average level of NO₂ in the homes of nonsmokers and smokers without gas-fired appliances was 12 and 15 μg/m³, respectively, in the summer. The corresponding winter values were 19 and 22 μg/m³. Furthermore, the individual levels of NO₂ in the homes of smokers were generally below both the adjacent outdoor level and the National Ambient Air Quality Standard limit for annual exposure.     

Personal monitoring for nitrogen dioxide exposure: Methodological considerations for a community study

Personal exposure to nitrogen dioxide (NO₂) and time spent in various locations were measured for 66 family members from 19 homes in the Portage, WI area during March 1981. Passive diffusion NO₂ monitors were placed outdoors, in the kitchen, and in one bedroom on each floor of the homes, and were worn by family members. Individuals from gas-cooking homes had significantly higher average NO₂ exposures than those from homes using electricity for cooking (mean difference 19.37 μg/m³). Personal exposures were more closely related to bedroom levels than to kitchen or outdoor concentrations for both cooking fuel groups. Several preliminary models are presented which relate average personal NO₂ exposure to indoor and ambient levels, and also to the proportion of time spent in different locations. These models are capable of explaining nearly 90% of the variation about the mean in personal exposure.     

Associations between short-term exposure to nitrogen dioxide and mortality in 17 Chinese cities: The China Air Pollution and Health Effects Study (CAPES)

Few multi-city studies in Asian developing countries have examined the acute health effects of ambient nitrogen dioxide (NO₂). In the China Air Pollution and Health Effects Study (CAPES), we investigated the short-term association between NO₂ and mortality in 17 Chinese cities. We applied two-stage Bayesian hierarchical models to obtain city-specific and national average estimates for NO₂. In each city, we used Poisson regression models incorporating natural spline smoothing functions to adjust for long-term and seasonal trend of mortality, as well as other time-varying covariates. We examined the associations by age, gender and education status. We combined the individual-city estimates of the concentration–response curves to get an overall NO₂–mortality association in China. The averaged daily concentrations of NO₂ in the 17 Chinese cities ranged from 26 μg/m³ to 67 μg/m³. In the combined analysis, a 10-μg/m³ increase in two-day moving averaged NO₂ was associated with a 1.63% [95% posterior interval (PI), 1.09 to 2.17], 1.80% (95% PI, 1.00 to 2.59) and 2.52% (95% PI, 1.44 to 3.59) increase of total, cardiovascular, and respiratory mortality, respectively. These associations remained significant after adjustment for ambient particles or sulfur dioxide (SO₂). Older people appeared to be more vulnerable to NO₂ exposure. The combined concentration–response curves indicated a linear association. Conclusively, this largest epidemiologic study of NO₂ in Asian developing countries to date suggests that short-term exposure to NO₂ is associated with increased mortality risk.     

Concentrations and determinants of outdoor, indoor and personal nitrogen dioxide in pregnant women from two Spanish birth cohorts

Determinants of outdoor, indoor and personal concentrations of nitrogen dioxide (NO₂) were assessed in a subset of pregnant women of the Spanish INMA (Environment and Childhood) Study. Home indoor and outdoor NO₂ concentrations were measured during 48 h with passive samplers for 50 and 58 women from the INMA cohorts of Valencia and Sabadell, respectively. Women from Sabadell also carried personal NO₂ samplers during the same period. Data on time–activity patterns, socio-economic characteristics, and environmental exposures were obtained through questionnaires. Multiple linear regression models were developed to predict NO₂ levels.In Valencia, median outdoor NO₂ levels (42 µg/m³) were higher than median indoor levels (36 µg/m³). In Sabadell, personal NO₂ showed the highest median levels (40 µg/m³), followed by indoor (32 µg/m³) and outdoor (29 µg/m³) levels. Personal exposure to NO₂ correlated best with the indoor NO₂ levels. Temporal and traffic-related variables were significant predictors for outdoor NO₂ levels. Thirty-two percent of the indoor NO₂ variability in the two cohorts was explained by outdoor NO₂ levels and the use of the gas appliances. The model for personal exposure accounted for 59% of the variance in NO₂ levels in Sabadell with four predictor variables (outdoor and indoor NO₂ levels, time spent in outdoor environments and time exposed to a gas cooker). No significant association was found between personal or indoor NO₂ levels and exposure to environmental tobacco smoke (ETS) at home.Personal NO₂ levels were found to be strongly influenced by indoor NO₂ concentrations. The study supports the use of time–activity patterns along with indoor measurements to predict personal exposure to traffic-related air pollution.     

Personal exposure monitoring to nitrogen dioxide

Measurement of personal exposure to nitrogen dioxide for short and long term was made with a sensitive NO₂ passive sampler by volunteer housewives and office workers in different seasons. These measurements were compared with the simultaneous measurement of outdoor and indoor concentration of the participants. A common result over all the measurements is the potential effect of using an unvented space heater to increase personal exposure. Mean personal exposure and indoor concentration are higher than outdoor levels elevated by the samples exposed to pollutant produced from the heater. Without an NO₂ source indoors, the mean outdoor concentrations are always highest among the data of measurement. A time-weighted indoor/outdoor activity model gives modestly improved estimates of personal exposure over those predicted from measured indoor concentrations alone.     

A method to derive the relationship between the annual and short-term air quality limits—Analysis using the WHO Air Quality Guidelines for health protection

The World Health Organization (WHO) Air Quality Guidelines (AQG) were launched in 2006, but gaps remain in evidence on health impacts and relationships between short-term and annual AQG needed for health protection. We tested whether relationships between WHO short-term and annual AQG for particulates (PM₁₀ and PM_2.5) and nitrogen dioxide (NO₂) are concordant worldwide and derived the annual limits for sulfur dioxide (SO₂) and ozone (O₃) based on the short-term AQG. We obtained air pollutant data over seven years (2004–2010) in seven cities from Asia-Pacific, North America and Europe. Based on probability distribution concept using maximum as the short-term limit and arithmetic mean as the annual limit, we developed a new method to derive limit value one from another in each paired limits for each pollutant with capability to account for allowable exceedances. We averaged the limit derived each year for each city, then used meta-analysis to pool the limit values in all cities. Pooled mean short-term limit for NO₂ (140.5 μg/m³ [130.6–150.4]) was significantly lower than the WHO AQG of 200 μg/m³ while for PM₁₀ (46.4 μg/m³ [95CI:42.1–50.7]) and PM_2.5 (28.6 μg/m³ [24.5–32.6]) were not significantly different from the WHO AQG of 50 and 25 μg/m³ respectively. Pooled mean annual limits for SO₂ and O₃ were 4.6 μg/m³ [3.7–5.5] and 27.0 μg/m³ [21.7–32.2] respectively. Results were robust in various sensitivity analyses. The distribution relationships between the current WHO short-term and annual AQG are supported by empirical data from seven cities for PM₁₀ and PM_2.5, but not for NO₂. The short-term AQG for NO₂ should be lowered for concordance with the selected annual AQG for health protection.     

An appraisal of emissions control requirements in the California South Coast Air Basin

The purpose of this study is to evaluate the effect of reductions of reactive organic gases (ROG) and NO_x emissions on short-term O₃ and NO₂ concentrations and annual average NO₂ concentrations in the California South Coast Air Basin. Short-term air quality predictions were obtained by applying the Systems Applications Airshed Model to summer O₃ and autumn NO₂ episodes. Effects of emission controls on annual NO₂ concentrations were estimated using CDM and a new parcel tracking model NOXTRAK. Results for the summer O₃ episode indicate that ROG emission reduction in an effective means for reducing peak O₃ concentrations. NO_x emission reduction imposed in addition to ROG emission reductions are counterproductive in reducing peak O₃ concentrations. The modeling results also suggest that attainment of the 1-h federal O₃ standard requires ROG emission reductions on the order of 80% from 1987 levels. Results for the autumn NO₂ episode indicate that NO_x emission reductions approximating those recommended in a proposed Air Quality Management Plan (about 22%) will result in only small (about 5%) reductions in the peak NO₂ concentrations. ROG emission reduction may be more effective than NO_x emission reduction in reducing the peak NO₂ concentration. For the episode studied, a reduction of 36% in ROG emissions is estimated to result in a reduction in peak NO₂ concentrations commensurate with that required to attain the 1-h state NO₂ standard. Model calculations also indicate that the federal NO₂ standard may not be meet by 1987 at one or two stations, but may blosely approached.     

Two-year follow-up study of nonregulatory recommendations for better air quality in indoor ice arenas

A standardized questionnaire was used in a two-year follow-up study to test the effectiveness of non-regulatory recommendations to improve indoor air quality of 103 ice arenas in Finland. In addition, the performance of a state-of-the-art emission control technology (ECT) on propane-fueled resurfacers was evaluated by measuring the one-week average nitrogen dioxide (NO₂) concentration in a small sample of arenas. The number of retrofitted ECT on propane-fueled resurfacers increased from 6 to 37 (8% to 37% of ice arenas) and the number of electric resurfacers from 7 to 9 (both 9% of arenas) in 1994–1996. At the same time, the prevalence of inadequate ventilation increased among the most susceptible small arenas (volume <30 000 m³) from 11 (31%) to 19 (38%). Combustion-powered resurfacers (88%) and inadequate ventilation (24%) were prevalent also among the 17 new arenas built in 1994–1996. ECT resurfacers significantly decreased the mean indoor NO₂ concentration of eleven arenas from 650 μg/m³ to 147 μg/m³. Thus, retrofitting resurfacers with ECT seems to be a feasible mitigation option to improve indoor air quality in ice arenas, but the ultimate solution is an electric ice resurfacer. Non-regulatory recommendations seem to be partially effective in abatement against the air quality problems, but additional regulatory measures are needed for full compliance in all arenas.     

A badge-type personal sampler for measurement of personal exposure to NO2 and NO in ambient air

A badge-type personal sampler was developed for measuring personal exposure to nitrogen dioxide (NO₂). An absorbent sheet containing triethanolamine (TEA) solution absorbed NO₂ which diffused through five layers of hydrophobic fiber filter. Wind effects on absorption rate were suppressed by these filter layers. NO₂ was measured by the sampler with a sensitivity of 124.8 μg h/m³ (66 ppb h) and an accuracy of within ± 20%. It could be used for measuring personal exposure to NO₂ without interfering with the wearer's daily activities. Nitric oxide (NO) could be measured after a small modification to the sampler provided oxidation ability to the layers of diffusion filter. Three layers of hydrophobic fiber filter were replaced by 12 layers of glass fiber filter containing chromium trioxide solution. NO was oxidized to NO₂ in the oxidation layers and absorbed by the absorbent sheet together with the coexisting NO₂. Sensitivity and accuracy of the sampler for NO were nearly equal to that for NO₂.     

Indoor air quality modeling: Compartmental approach with reactive chemistry

Data on indoor/outdoor pollutant and tracer concentrations were collected during different periods in 1981 at a residence in Newton, MA. Special studies within the kitchen were conducted to determine the vertical and horizontal variability of pollutant and tracer gas concentrations. A reactive chemistry model incorporating simplified NO_x chemistry was developed to simulate pollutant concentrations indoors. Multicompartmental mathematical modeling tools were also developed and tested to estimate efficiently the effective, emission, ventilation, and removal rates, as well as the intercompartmental pollutant exchange coefficients. Model studies utilizing two- and three-compartment systems and tracer measurements proved that the dynamics of pollutant mixing inside a kitchen is not only complex but may be quite important in controlling spatial and temporal variability of reactive species. Further monitoring and modeling studies to investigate the critical aspects of the short-term dynamics of the reactive pollutants inside homes with gas cooking stoves are recommended.     

Atmospheric releases from fossil fuel power plants in the United States

This paper contains detailed data on atmospheric emissions from power plants with a capacity of more than 25 MW electric in the United States. The data are gathered from utility files as presented to the U.S. Environmental Protection Agency. Pollutants covered are CO, NO_x, SO_x3, particulates, and total hydrocarbons. The data indicate that in 1977 about 420×10⁹ kg coal, 84×10⁶ m³ oil, and 65×10⁶ m³ of natural gas were used to generate electricity. Pollutants generated were 2×10⁹kg particulates, 17×10⁹ kg SO₂, 6×10⁹ kg NO_x, 78×10⁶ kg hydrocarbons and 0.3×10⁶ kg of CO.     

Seasonal variation in outdoor,indoor, and personal air pollution exposures of women using wood stoves in the Tibetan Plateau: Baseline assessment for an energy intervention study

Cooking and heating with coal and biomass is the main source of household air pollution in China and a leading contributor to disease burden. As part of a baseline assessment for a household energy intervention program, we enrolled 205 adult women cooking with biomass fuels in Sichuan, China and measured their 48-h personal exposure to fine particulate matter (PM_2.5) and carbon monoxide (CO) in winter and summer. We also measured the indoor 48-h PM_2.5 concentrations in their homes and conducted outdoor PM_2.5 measurements during 101 (74) days in summer (winter). Indoor concentrations of CO and nitrogen oxides (NO, NO₂) were measured over 48-h in a subset of ~ 80 homes. Women's geometric mean 48-h exposure to PM_2.5 was 80 μg/m³ (95% CI: 74, 87) in summer and twice as high in winter (169 μg/m³ (95% CI: 150, 190), with similar seasonal trends for indoor PM_2.5 concentrations (winter: 252 μg/m³; 95% CI: 215, 295; summer: 101 μg/m³; 95% CI: 91, 112). We found a moderately strong relationship between indoor PM_2.5 and CO (r = 0.60, 95% CI: 0.46, 0.72), and a weak correlation between personal PM_2.5 and CO (r = 0.41, 95% CI: − 0.02, 0.71). NO₂/NO ratios were higher in summer (range: 0.01 to 0.68) than in winter (range: 0 to 0.11), suggesting outdoor formation of NO₂ via reaction of NO with ozone is a more important source of NO₂ than biomass combustion indoors. The predictors of women's personal exposure to PM_2.5 differed by season. In winter, our results show that primary heating with a low-polluting fuel (i.e., electric stove or wood-charcoal) and more frequent kitchen ventilation could reduce personal PM_2.5 exposures. In summer, primary use of a gaseous fuel or electricity for cooking and reducing exposure to outdoor PM_2.5 would likely have the greatest impacts on personal PM_2.5 exposure.     

Associations of gestational and early life exposures to ambient air pollution with childhood respiratory diseases in Shanghai,China: A retrospective cohort study

BackgroundAssociations of ambient air pollutants with respiratory health are inconsistent.ObjectivesWe analyzed the associations of gestational and early life exposures to air pollutants with doctor-diagnosed asthma, allergic rhinitis, and pneumonia in children.MethodsWe selected 3358 preschool children who did not alter residences after birth from a cross-sectional study in 2011–2012 in Shanghai, China. Parents reported children's respiratory health history, home environment, and family lifestyle behaviors. We collected daily concentrations of sulphur dioxide (SO₂), nitrogen dioxide (NO₂), and particulate matter with an aerodynamic diameter ≤ 10 μm (PM₁₀) during the child's total lifetime (2006–2012) for each district where the children lived. We analyzed the associations using logistic regression models.ResultsAfter adjusting for covariates and the other studied pollutants, we found that exposure to NO₂ (increment of 20 μg/m³) during the first year of life was significantly associated with asthma [odds ratio (OR) = 1.77; 95% confidence interval (CI): 1.29–2.43] and allergic rhinitis (OR = 1.67; 95% CI: 1.07–2.61). Exposure to NO₂ during gestation, the first two and three years, and over total lifetimewas all consistently associated with increased odds of allergic rhinitis. Quartiles of NO₂ concentration during different exposure periods showed a slight dose–response relationship with the studied diseases. These diseases had significant associations with pollutant mixtures that included NO₂, but had no significant association with exposures to SO₂ and PM₁₀ individually or in mixtures.ConclusionsGestational and early life exposures to ambient NO₂ are risk factors for childhood respiratory diseases.     

Odor-annoyance estimates from roadtraffic combustion exhausts: Calibration with master scaling using pyridine as a reference

The present field study addressed the need for a procedure that provides a defined unit of measurement of perceived annoyance from environmental odors, calibrating the estimates for individual scaling behavior and context effects. In including 25 subjects, the purpose was to demonstrate the applicability of the master-scale procedure with magnitude estimation to perform such a calibration of odor-annoyance estimates for target stimuli such as road-traffic combustion exhausts (13 000 vehicles/d; averaging 47 μg/m³ over the day/night with peaks exceeding 100 μg/m³ of nitrogen dioxide; NO₂). For comparison, calibrated estimates were also obtained for a backyard expected to be considerably less polluted (comparable with 18 μg/m³ of NO₂) and for blank stimuli presented indoors. The data transformation for the calibration procedure with which annoyance is expressed in either master-scale units or pyridine equivalents requires estimates of a reference stimulus for which seven concentrations of pyridine were used. The results provide an illustration of master scaling of odor annoyance, and imply that use of a modulus (standard stimulus with a predefined annoyance magnitude), in contrast to master scaling, is not sufficient for calibration for individual scaling behavior and context effects.     

Effect of sample conditioning and chamber loading on rate of formaldehyde release from wood products in a desiccator test

Several variables may influence the observed rate of formaldehyde (CH₂O) offgassing from wood products in a small static test chamber. We studied the effect of sample conditioning at ≈100% relative humidity and chamber loading (sample size) on CH₂O release rate from particle board (PB) and plywood (PW). Samples of PB and PW were placed in glass desiccators with reservoirs of water at a loading of 21 m²/m³ (sample surface area per chamber volume). The rate of CH₂O offgassing from the PB did not change over several weeks under these conditions (0.24 μg/cm²/day), but the overall release rate from the PW decreased after 8 days. In another experiment, the loading of the desiccator had a major effect on the rate of CH₂O offgassing from PB over a loading range of 1 to 42 m²/m³. The same phenomenon was observed with different loadings of PW. The inverse of the observed release rate varied linearly with the chamber loading of PB or PW. At a loading which may be encountered in a house (0.25 m²/m³), the release rate coefficient for PB calculated from the above inverse relation was 22-fold higher than that measured at a more conventional test load of 21 m²/m³. These results indicate that great care should be exercised when using desiccator tests for assessing and comparing the potential strength of materials as sources of CH₂O in the indoor environment.     

Ambient air pollution and children's lung function in China

ObjectiveTo describe the correlations between ambient air pollutants (TSP, SO₂, NO_x) and the level of children's lung function (FVC, FEV₁, MMEF) in China.MethodsWe collected the research articles on ambient air pollution and children's lung function published from 1985 to 2006 and selected 11 articles finally according to the following criteria: (1) Children between the age of 7 and 15 as objects; (2) Local air quality monitoring results were reported; (3) Strict quality control was taken when testing children's lung function; (4) The results were expressed by the average of measured value. Then we analyzed the correlation relationship between the level of ambient air pollutants and children's lung function and compared the effects of ambient air pollutants on children's lung function of boy and girl.ResultsThe selected articles included the results of 7 cities in China. Among them, the results of 6 cities' studies revealed that the levels of children's lung function were significantly lower in the areas with heavy ambient air pollution than those in the areas with light ambient air pollution. According to the articles, the average levels of TSP were at the range of 0.084 mg/m³–0.835 mg/m³, SO₂ were 0.013 mg/m³–0.929 mg/m³, NO_x were 0.044 mg/m³–0.229 mg/m³. Correlation analysis showed significant negative correlation between the levels of TSP and SO₂ and children's FVC and FEV₁, as well as the levels of NO_x and children's MMEF. The correlation coefficient was ? 0.797 (t = ? 4.384, P = 0.001) between TSP and FVC, ? 0.693 (t = ? 4.190, P < 0.001) between Ln (SO₂) and FVC, ? 0.886 (t = ? 5.392, P = 0.001) and ? 0.685 (t = ? 4.101, P = 0.001) between FEV₁ and TSP and Ln (SO₂), and ? 0.973 (t = ? 5.993, P = 0.027) between NO_xNO_x and MMEF, respectively. The results also suggested that the decreases of lung function for girl with the increasing of ambient air pollution were significantly greater for boy.ConclusionThe levels of ambient air TSP and SO₂ correlated with the damage of the big airway function of children, while NO_xNO_x affected the small airway function chiefly. Furthermore, lung function of girl was more susceptible to ambient air pollutants than boy.     

Screening of household products for the emission of volatile organic compounds

10 household products, eight waxes or polishes, and two detergents have been screened by a headspace technique for the emission of volatile organic compounds (VOC). Using Tenax sampling and analysis by combined gas chromatography-mass spectrometry (GC-MS) more than 80 single compounds or groups of isomers have been identified, and semiquantitative data on the initial emission rates (emission rate immediately after application) have been obtained. Products fall into two groups: those containing water as a main (80 to 90%) constituent and those without water. The initial emission rate of the first group ranged from 0.2 to 2 μg cm⁻²min⁻¹, whereas the second group had higher emission rates of up to 430 μg cm⁻²min⁻¹. Products of the second group emit essentially hydrocarbons (alkanes, alkenes, and terpenes), whereas most products of the first group emit oxygenated compounds including terpene alcohols and their acetates, aliphatic alcohols and esters, and alkoxy-alcohols.     

Temporal and spatial distribution of Cs in Eastern Mediterranean Sea. Horizontal and vertical dispersion in two regions

Caesium-137 activity concentration in the water columns of the Gulf of Patras (Central Greece) and the North-Eastern Aegean Sea (easterward to Lemnos Island) was investigated in selected sampling stations during the period September 2004–June 2006. The methodology followed was based on the sorption of caesium (Cs) on cotton wound cartridge filters impregnated by Cu₂[Fe(CN)₆] via in-situ pumping. In terms of the horizontal and vertical records, the activity concentrations of ¹³⁷Cs in the Gulf of Patras ranged between 1.2 and 6.7 Bq m⁻³, depending on the sampling period and the prevailing physicochemical regime at the sampling station. The general pattern of the decreased activity concentrations of ¹³⁷Cs with increasing depth was reversed in the Gulf of Patras during the cold period attributed to the prevailing advective processes of the area. The activity concentrations of ¹³⁷Cs in the North-Eastern Aegean Sea ranged from 2.6 to 12.8 Bq m⁻³, whereas significant stratified curves were observed during the warm period and also, in one station during the cold period. In terms of temporal variation, the discharges in the Gulf of Patras resulted in enhanced levels of ¹³⁷Cs, whereas in the North Aegean Sea the incoming water masses form the Black Sea had an apparent influence throughout the year by increasing the ¹³⁷Cs levels, hence presenting a weak seasonal variation. Comparing the two studied areas, one could say that the North Aegean Sea, as an open sea environment, presented higher concentrations due to the influence of the Black Sea water masses. The estimated inventories of ¹³⁷Cs in the Gulf of Patras ranged 0.25 ± 0.03–0.79 ± 0.03 kBq m⁻², whereas in the North-Eastern Aegean Sea they ranged 0.33 ± 0.02–0.92 ± 0.03 kBq m⁻².     

Carbon fluxes from coarse woody debris in southern taiga forests of the Valdai Upland

Studies in three typical forest biotopes of the Valdai Upland were performed to evaluate the stocks and surface area of coarse woody debris from spruce and birch (in linear transects), its colonization by xylotrophic fungi (during reconnaissance surveys), and CO₂ emission (by a chamber method). The stock and surface area were minimum in a paludal birch forest (46.4 m³/ha and 960 m²/ha) and maximum in a decay area of spruce forest (256.1 m³/ha and 3761 m²/ha, respectively). The assemblages of wood-decay fungi had a composition typically found in southern taiga forests. The total CO₂ flux varied from 145 kg C-CO₂/ha per year in the paludal birch forest to 462 kg C-CO₂/ha per year in small herb–green moss spruce forest. It is concluded that air temperature is an informative predictor of seasonal C-CO₂ flux rate from coarse woody debris.     

Ecological effects of experimental oil spills in Eastern coastal plain estuaries

Ecological effects of weathered and unweathered Louisiana crude oil spilled in eastern coastal plain estuaries were evaluated at all trophic levels and the major chemical components of the oil were followed through selected components of the ecosystem for 36 months.The study site consisted of a natural estuarine marshcreek habitat off the York River, Virginia, modified by the construction of retaining walls to form aquatic and marsh areas in each experimental unit. Each system was closed on all sides with the exception of an opening below the level of lowest tide to allow communication with tidal flow. Five experimental units were constructed, each having a surface area of about 810 m², containing 695 m² of marsh, 100 m² of open water and 15 m² of intertidal mud flat. The most upstream unit served as the control and the four downstream units received dosages of fresh and weathered crude oil. In addition, biological sampling in the open marsh and creek areas was conducted to provide an estimate of the effects of containing the marsh.Five hundred and seventy liters of fresh South Louisiana crude were added to each of the two downstream experimental enclosures approximately three hours into flood tide and were completed in 1 h. The weathered oil was similarly applied to the upstream units 3 days later.The weathered oil was not visible one week after the spill except as coatings on marsh grass blades, while the fresh crude remained for over three weeks. Plankton populations recovered within a week, and fish mortalities, which were most pronounced in the weathered oil unit, ceased after 10 days.Reductions in standing crops of marsh grasses were most pronounced the year following the spills, when peak biomass in the control exceeded the spill units by a factor of three. Recovery progressed further in the second year with peak biomass in the oiled units being about 70% of the control. The third year following the spill, recovery was nearly complete.Benthic populations were dominated numerically by oligochaetes. Significant reductions in populations of this dominant organisms and in populations of polychaetes and amphipods were demonstrable for a period of three years although most of the populations have shown definite signs of recovery.