Quantifying traffic, biomass burning and secondary source contributions to atmospheric particle number concentrations at urban and suburban sites.

In this study, we propose a new approach to determine the contributions of primary vehicle exhaust (N1ff), primary biomass burning (N1bb) and secondary (N2) particles to mode segregated particle number concentrations. We used simultaneous measurements of aerosol size distribution in the 12-600 nm size range and black carbon (BC) concentration obtained during winter period at urban and suburban sites influenced by biomass burning (BB) emissions. As expected, larger aerosol number concentrations in the 12-25 and 25-100 nm size ranges are observed at the urban site compared to the suburban site. However, similar concentrations of BC are observed at both sites due to the larger contribution of BB particles to the observed BC at suburban (34%) in comparison to urban site (23%). Due to this influence of BB emissions in our study area, the application of the Rodríguez and Cuevas (2007) method, which was developed for areas mainly influenced by traffic emissions, leads to an overestimation of the primary vehicle exhaust particles concentrations by 18% and 26% in urban and suburban sites, respectively, as compared to our new proposed approach. The results show that (1) N2 is the main contributor in all size ranges at both sites, (2) N1ff is the main contributor to primary particles (>70%) in all size ranges at both sites and (3) N1bb contributes significantly to the primary particles in the 25-100 and 100-600 nm size ranges at the suburban (24% and 28%, respectively) and urban (13% and 20%, respectively) sites. At urban site, the N1ff contribution shows a slight increase with the increase of total particle concentration, reaching a contribution of up to 65% at high ambient aerosol concentrations. New particle formation events are an important aerosol source during summer noon hours but, on average, these events do not implicate a considerable contribution to urban particles.

Organophosphate esters in airborne particles from subway stations.

For the first time, the concentrations of 19 organophosphate esters (OPEs) were measured in airborne fine particulate matter (PM2.5) from subway stations in Barcelona (Spain) to investigate their occurrence, contamination profiles and associated health risks. OPEs were detected in all PM2.5 samples with levels ranging between 1.59 and 202 ng/m3 (mean value of 39.9 ng/m3). Seventeen out of 19 tested analytes were detected, with TDClPP, TClPP and TCEP being those presenting the highest concentrations. OPE concentrations are not driven by the same factors that determine the ambient PM2.5 concentrations of other constituents in the subway. Newer stations presented higher OPE levels, probably due to the materials used in the design of the platforms, with greater use of modern plastic materials versus older stations with tiles and stones. Estimated daily intakes via airborne particles inhalation during the time expended in subway stations were calculated, as well as the carcinogenic and non-carcinogenic health risks (CR and non-CR), all being much lower than the threshold risk values. Thus, subway inhalation exposure when standing on the platform to OPE's per se is not considered to be dangerous for commuters.

Evaluation of the Semi-Continuous OCEC analyzer performance with the EUSAAR2 protocol.

This work evaluates the applicability of the reference protocol EUSAAR2 in the Semi-Continuous OCEC analyzer under two environments, an urban background site influenced by traffic emissions and a regional background site. The comparison of the 24-h averaged OC and EC measurements of the Semi-Continuous analyzer with the OC and EC concentrations determined offline in PM2.5 24 h filters yielded very good agreement for both denuded and undenuded samples. In the urban background site, the regression for EC yielded a slope of 0.93 and 1.04 (b = 0.07 and 0.05, R2 = 0.83 and 0.84), for denuded and undenuded samples respectively. The slopes of OC regressions were 0.99 (b = -0.18, R2 = 0.81) for the low volume and 0.93 (b = 0.12, R2 = 0.84) for the high volume samples. In the regional background site, the slopes of the EC regression with the denuded and undenuded samples was 0.91 and 1.02 correspondingly (b = 0 and - 0.03, R2 = 0.77 and 0.89). The regression of OC had slopes close to 1; 1.03 for the high volume and 0.95 for the low volume sampler (b = 0.08 and 0.26, R2 = 0.78 and 0.78). BC measurements obtained by an aethalometer and MAAP were in very good agreement with EC at both sampling sites. BC levels were consistently higher than EC (slope of the regression aethalometer BC vs EC slope a = 1.2, intercept b = 0.19, R2 = 0.79, for the urban background site and a = 1.9, b = -0.04, R2 = 0.94, for the regional site, slope MAAP BC vs EC a = 1.2, b = 0.06, R2 = 0.94, for the urban background site and 1.7, b = -0.03, R2 = 0.96, for the regional site). This confirms the need of using the site-specific mass absorption cross section (MAC) instead of the ones provided by manufacturers for the conversion of absorption units into BC mass concentration. BC data correlated very well with the optical EC obtained from the semi-continuous OCEC analyzer (a = 1.3, b = 0.16, R2 = 0.80 for the urban background site and a = 1.7, b = 0.009, R2 = 0.94 for the regional site, respectively). The comparison of OC concentrations by the Semi-Continuous Sunset analyzer with organic aerosol online measurements by ACSM showed strong correlations. The ratio OA/OC was 1.9 and 2.3 for the urban background and regional sites. The accumulation of refractory material on the filter, because of prolonged periods of sampling, caused a shift of the split point to the inert mode and changes on PC formation and evolution. Extreme dust outbreaks lead to the overestimation of OC due to the evolution of carbonate in the He mode. Generally, the Sunset Semi-Continuous OCEC analyzer with EUSAAR2 provided robust and consistent measurements with offline thermal-optical analysis.

Vertical and horizontal fall-off of black carbon and NO2 within urban blocks.

While exposure to traffic pollutants significantly decreases with distance from the curb, very dense urban architectures hamper such dispersion. Moreover, the building height reduces significantly the dispersion of pollutants. We have investigated the horizontal variability of Black Carbon (BC) and the vertical variability of NO2 and BC within the urban blocks. Increasing the distance from road BC concentrations decreased following an exponential curve reaching halving distances at 25 m (median), although with a wide variability among sites. Street canyons showed sharper fall-offs than open roads or roads next to a park. Urban background concentrations were achieved at 67 m distance on average, with higher distances found for more trafficked roads. Vertical fall-off of BC was less pronounced than the horizontal one since pollutants homogenize quickly vertically after rush traffic hours. Even shallower vertical fall-offs were found for NO2. For both pollutants, background concentrations were never reached within the building height. A street canyon effect was also found exacerbating concentrations at the lowest floors of the leeward side of the road. These inputs can be useful for assessing population exposure, air quality policies, urban planning and for models validation.

Health risk assessment from exposure to particles during packing in working environments.

Packing of raw materials in work environments is a known source of potential health impacts (respiratory, cardiovascular) due to exposure to airborne particles. This activity was selected to test different exposure and risk assessment tools, aiming to understand the effectiveness of source enclosure as a strategy to mitigate particle release. Worker exposure to particle mass and number concentrations was monitored during packing of 7 ceramic materials in 3 packing lines in different settings, with low (L), medium (M) and high (H) degrees of source enclosure. Results showed that packing lines L and M significantly increased exposure concentrations (119-609 µg m-3 respirable, 1150-4705 µg m-3 inhalable, 24,755-51,645 cm-3 particle number), while non-significant increases were detected in line H. These results evidence the effectiveness of source enclosure as a mitigation strategy, in the case of packing of ceramic materials. Total deposited particle surface area during packing ranged between 5.4 and 11.8 × 105 µm2 min-1, with particles depositing mainly in the alveoli (51-64%) followed by head airways (27-41%) and trachea bronchi (7-10%). The comparison between the results from different risk assessment tools (Stoffenmanager, ART, NanoSafer) and the actual measured exposure concentrations evidenced that all of the tools overestimated exposure concentrations, by factors of 1.5-8. Further research is necessary to bridge the current gap between measured and modelled health risk assessments.

Aerosol sources in subway environments.

Millions of people use rail subway public transport around the world, despite the relatively high particulate matter (PM) concentrations in these underground environments, requiring the identification and quantification of the aerosol source contributions to improve the air quality. An extensive aerosol monitoring campaign was carried out in eleven subway stations in the Barcelona metro system, belonging to seven subway lines. PM2.5 samples were collected during the metro operating hours and chemically analysed to determine major and trace elements, inorganic ions, and total carbon. The chemical compositions of subway components such as brake pads, rail tracks and pantographs were also determined. The mean PM2.5 concentrations varied widely among stations, ranging from 26 µg m-3 to 86 µg m-3. Subway PM2.5 was mainly constituted by Fe2O3 (30-66%), followed by carbonaceous matter (18-37%) for the old stations, while for new stations equipped with Platform Screen Doors (PSD) these percentages go down to 21-44% and 15-30%, respectively. Both the absolute concentrations and the relative abundance of key species differed for each subway station, although with common patterns within a given subway line. This is a result of the different emission chemical profiles in different subway lines (using diverse types of brakes and/or pantographs). The co-emission of different sources poses a problem for their separation by receptor models. Nevertheless, receptor modelling (Positive Matrix Factorization) was applied resulting in ten sources, five of them subway-specific: RailWheel, RailWheel+Brake, Brake_A, Brake_B, Pb. The sum of their contributions accounted for 43-91% of bulk PM2.5 for the old stations and 21-52% for the stations with PSD. The decrease of the activity during the weekends resulted in a decrease (up to 56%) in the subway-specific sources contribution to the -already lower- bulk PM2.5 concentrations compared to weekdays. The health-related elements are mainly apportioned (> 60%) by subway sources.

Bioaerosols in the Barcelona subway system.

Subway systems worldwide transport more than 100 million people daily; therefore, air quality on station platforms and inside trains is an important urban air pollution issue. We examined the microbiological composition and abundance in space and time of bioaerosols collected in the Barcelona subway system during a cold period. Quantitative PCR was used to quantify total bacteria, Aspergillus fumigatus, influenza A and B, and rhinoviruses. Multitag 454 pyrosequencing of the 16S rRNA gene was used to assess bacterial community composition and biodiversity. The results showed low bioaerosol concentrations regarding the targeted microorganisms, although the bacterial bioburden was rather high (104 bacteria/m3 ). Airborne bacterial communities presented a high degree of overlap among the different subway environments sampled (inside trains, platforms, and lobbies) and were dominated by a few widespread taxa, with Methylobacterium being the most abundant genus. Human-related microbiota in sequence dataset and ascribed to potentially pathogenic bacteria were found in low proportion (maximum values below 2% of sequence readings) and evenly detected. Hence, no important biological exposure marker was detected in any of the sampled environments. Overall, we found that commuters are not the main source of bioaerosols in the Barcelona subway system.

Formation and alteration of airborne particles in the subway environment.

Most particles in the rail subway environment are sub-micron sized ferruginous flakes and splinters generated mechanically by frictional wear of brake pads, wheels and rails. To better understand the mechanisms of formation and the alteration processes affecting inhalable particles in subways, PM samples (1-2.5 µm and 2.5-10 µm) were collected in the Barcelona Metro and then studied under a scanning electron microscope. Most particles in these samples are hematitic (up to 88%), with relatively minor amounts of mineral matter (up to 9%) and sulphates (up to 5%). Detailed microscopy (using back scattered and TEM-DRX imaging) reveals how many of the metallic particles comprise the metallic Fe nucleus surrounded by hematite (Fe2O3) and a coating of sulphate and chloride salts mixed with mineral matter (including Ca-carbonates, clay minerals and quartz). These observations record the emission of fine to ultrafine FePM by frictional wear at elevated temperatures that promote rapid partial (or complete) oxidation of the native metal. Water condensing on the PM surface during cooling leads to the adsorption of inorganic mineral particles that coat the iron oxide. The distinctively layered polymineralic structure that results from these processes is peculiar to particles generated in the subway environment and very different from PM typically inhaled outdoors.

Secondary organic aerosol origin in an urban environment: influence of biogenic and fuel combustion precursors.

Source contributions of organic aerosol (OA) are still not fully understood, especially in terms of quantitative distinction between secondary OA formed from anthropogenic precursors vs. that formed from natural precursors. In order to investigate the OA origin, a field campaign was carried out in Barcelona in summer 2013, including two periods characterized by low and high traffic conditions. Volatile organic compound (VOC) concentrations were higher during the second period, especially aromatic hydrocarbons related to traffic emissions, which showed a marked daily cycle peaking during traffic rush hours, similarly to black carbon (BC) concentrations. Biogenic VOC (BVOC) concentrations showed only minor changes from the low to the high traffic period, and their intra-day variability was related to temperature and solar radiation cycles, although a decrease was observed for monoterpenes during the day. The organic carbon (OC) concentrations increased from the first to the second period, and the fraction of non-fossil OC as determined by (14)C analysis increased from 43% to 54% of the total OC. The combination of (14)C analysis and Aerosol Chemical Speciation Monitor (ACSM) OA source apportionment showed that the fossil OC was mainly secondary (>70%) except for the last sample, when the fossil secondary OC only represented 51% of the total fossil OC. The fraction of non-fossil secondary OC increased from 37% of total secondary OC for the first sample to 60% for the last sample. This enhanced formation of non-fossil secondary OA (SOA) could be attributed to the reaction of BVOC precursors with NOx emitted from road traffic (or from its nocturnal derivative nitrate that enhances night-time semi-volatile oxygenated OA (SV-OOA)), since NO2 concentrations increased from 19 to 42 µg m(-3) from the first to the last sample.

2001-2012 trends on air quality in Spain.

This study aims at interpreting the 2001-2012 trends of major air pollutants in Spain, with a major focus on evaluating their relationship with those of the national emission inventories (NEI) and policy actions. Marked downward concentration trends were evidenced for PM10, PM2.5 and CO. Concentrations of NO2 and NOx also declined but in a lesser proportion at rural and traffic sites. At rural sites O3 has been kept constant, whereas it clearly increased at urban and industrial sites. Comparison of the air quality trends and major inflection points with those from NEIs, the National Energy Consumption and the calendar of the implementation of major policy actions allowed us to clearly identify major benefits of European directives on power generation and industrial sources (such as the Large Combustion Plants and the Integrated Pollution Prevention and Control Directives). This, together with a sharp 2007-2008 decrease of coal consumption has probably caused the marked parallel decline of SO2, NOx and for PM2.5 concentrations. Also the effect of the EURO 4 and 5 vehicle emission standards on decreasing emissions of PM and CO from vehicles is noticeable. The smooth decline in NO2-NOx levels is mostly attributed to the low efficiency of EURO 4 and 5 standards in reducing real life urban driving NO2 emissions. The low NOx decrease together with the complexity of the reactions of O3 formation is responsible for the constant O3 concentrations, or even the urban increase. The financial crisis has also contributed to the decrease of the ambient concentration of pollutants; however this caused a major reduction of the primary energy consumption from 2008 to 2009, and not from 2007 to 2008 when ambient air PM and SO2 sharply decreased. The meteorological influence was characterized by a 2008-2012 period favorable to the dispersion of pollutants when compared to the 2001-2007.

Within-city contrasts in PM composition and sources and their relationship with nitrogen oxides.

The present work is part of the INMA (INfancia y Medio Ambiente -'Environment and Childhood') project, which aims at assessing the adverse effects of exposure to air pollution during pregnancy and early in life. The present study was performed in the city of Sabadell (Northeast Spain) at three sampling sites covering different traffic characteristics, during two times of the year. It assesses time and spatial variations of PM(2.5) concentrations, chemical components and source contributions, as well as gaseous pollutants. Furthermore, a cross-correlation analysis of PM components and source contributions with gaseous pollutants used as a proxy for exposure assessment is carried out. Our data show the influence of traffic emissions in the Sabadell area. The main PM sources identified by Positive Matrix Factorisation (PMF) were similar between the two seasons: mineral source (traffic-induced resuspension, demolition/construction and natural background), secondary sulphate (higher in summer), secondary nitrate (only during winter), industrial, and road traffic, which was the main contributor to PM(2.5) at two of the sites. The correlation of concentrations of nitrogen oxides was especially strong with those of elemental carbon (EC). The relatively weaker correlations with organic carbon (OC) in summer are attributed to the variable formation of secondary OC. Strong correlations between concentration of nitrogen oxides and PM(2.5) road traffic contributions obtained from source apportionment analysis were seen at all sites. Therefore, under the studied urban environment, nitrogen oxides can be used as a proxy for the exposure to road traffic contribution to PM(2.5); the use of NO(x) concentrations being preferred, with NO and NO(2) as second and third options, respectively.

Fine and coarse PM composition and sources in rural and urban sites in Switzerland: local or regional pollution?

The chemical composition and sources of ambient particulate matter (PM) in Switzerland were studied. PM(1) and PM(10) samples were collected in winter and summer at an urban background site in Zurich and a rural background site in Payerne. Concentrations of major and trace elements, NO(3)(-), SO(4)(2-), NH(4)(+), organic and elemental carbon were determined. A subsequent Positive Matrix Factorization (PMF) analysis was performed. PM(10) and PM(1) concentrations varied similarly at both sites, with average PM(10) concentrations 24-25 µg/m(3) and 13-14 µg/m(3) in winter and summer, respectively, and average PM(1) concentrations 12-17 µg/m(3) and 6-7 µg/m(3). The influence of local sources was found to be higher in winter. PM was dominated by nitrate and organic matter in winter, and by mineral matter and organic matter in summer. Trace element concentrations related to road traffic (Zn, Cu, Sb, Sn) were higher at Zurich. Concentrations of Tl and Cs, attributed to the influence of a glass industry, were higher at Payerne. The elements mainly present in the coarse fraction were those related to mineral matter and brake and tyre abrasion (Cu, Mn, Ti, Sb, Sr, Bi, Li, La, Nd), and those in the fine fraction were related to high temperature anthropogenic processes (Pb, As, Cd, Tl, Cs). Common PM(1) and PM(1-10) sources identified by PMF were: ammonium nitrate, present in winter, negligible in summer; ammonium sulfate+K(biomass burning)+road traffic; and road traffic itself, related to exhaust emissions in PM(1) and to road dust resuspension in PM(1-10). Size-fraction specific sources were: a PM(1) glass industry source characterized by Cs, Tl, Rb, Li and Na, only present in Payerne; a PM(1) background source characterized by V, Ni, sulfate and Fe; two PM(1-10) mineral-related sources, with higher contribution in summer; a PM(1-10) salt source; and a PM(1-10) organic source, with higher contribution in summer, attributed to bioaerosols.

Impact of fugitive emissions in ambient PM levels and composition: a case study in Southeast Spain.

The results of this study show the high impact that anthropogenic fugitive emissions of mineral dust have on air quality (levels of PM(10), PM(2.5) and some metals) in a region in SE Spain named L'Alacantí. This could be extensive to other areas of Europe with similar characteristics. Fugitive emissions, such as those arising from large public construction works, cement and ceramic manufacturing, mining, heavy industries, handling and transport of powdered raw materials and road dust, are very often left out of emission monitoring and inspections in Europe. The comparative study of daily PM(10) series in the area shows how the increase of annual average PM(10) concentrations over 40 microg/m(3) is due to extreme episodes occurring in 2006 and 2007, at a regional scale, given the simultaneous recording of PM episodes at distant monitoring sites. The annual average values of the PM(10) concentrations were close to or slightly higher than 40 microg/m(3) (limit value of Directive 2008/50/CE) during 2006-2007 (Alicante-University 39-41, Agost 40-42, Sant Vicent 42-46, Alicante-El Plà 40-42 microg/m(3)). The main PM(10) sources in the zone were identified with the assistance of the PMF receptor model. Six common factors were determined, mineral as a main source (37% at Agost and 32% at Sant Vicent), road traffic, secondary sulfate, petroleum coke, sea spray and industry. Mineralogical studies, with XRD and SEM-EDX techniques, support the hypothesis that the highest PM episodes are associated to fugitive emissions of mineral matter. Despite the fact that L'Alacantí region is a heavily industrialized area with two cement plants and a significant number of ceramic manufacturing plants, the fugitive emissions may have accounted for the exceedances of the PM limit values during these two years, part of them caused by the construction of a highway. These results may contribute to the interpretation of prior studies on source apportionment carried out in Southern Europe, with very high loads of anthropogenic dust in PM(10) and PM(2.5).

Organic compound characterization and source apportionment of indoor and outdoor quasi-ultrafine particulate matter in retirement homes of the Los Angeles Basin.

UNLABELLED: Quasi-ultrafine (quasi-UF) particulate matter (PM(0.25)) and its components were measured in indoor and outdoor environments at four retirement communities in Los Angeles Basin, California, as part of the Cardiovascular Health and Air Pollution Study (CHAPS). The present paper focuses on the characterization of the sources, organic constituents and indoor and outdoor relationships of quasi-UF PM. The average indoor/outdoor ratios of most of the measured polycyclic aromatic hydrocarbons (PAHs), hopanes, and steranes were close to or slightly lower than 1, and the corresponding indoor-outdoor correlation coefficients (R) were always positive and, for the most part, moderately strong (median R was 0.60 for PAHs and 0.74 for hopanes and steranes). This may reflect the possible impact of outdoor sources on indoor PAHs, hopanes, and steranes. Conversely, indoor n-alkanes and n-alkanoic acids were likely to be influenced by indoor sources. A chemical mass balance model was applied to both indoor and outdoor speciated chemical measurements of quasi-UF PM. Among all apportioned sources of both indoor and outdoor particles, vehicular emissions was the one contributing the most to the PM(0.25) mass concentration measured at all sites (24-47% on average). PRACTICAL IMPLICATIONS: Although people (particularly the elderly retirees of our study) generally spend most of their time indoors, a major portion of the PM(0.25) particles they are exposed to comes from outdoor mobile sources. This is important because, an earlier investigation, also conducted within the Cardiovascular Health and Air Pollution Study (CHAPS), showed that indoor-infiltrated particles from mobile sources are more strongly correlated with adverse health effects observed in the elderly subjects living in the studied retirement communities compared with other particles found indoors (Delfino et al., 2008).

Spatial and temporal variations in inhalable CuZnPb aerosols within the Mexico City pollution plume.

We report on the CuPbZn content of PM10 and PM2.5 samples collected from three sites (urban T0, suburban T1 and rural T2) during the Mexico City MILAGRO campaign of March 2006. Daytime city centre concentrations of summation operator CuZnPb(PM10) were much higher (T0 > 450 ng m(-3)) than at the suburban site (T1 < 200 ng m(-3)). Rural site (T2) summation operator CuZnPb(PM10) concentrations exceeded 50 ng m(-3) when influenced by the megacity plume but dropped to 10 ng m(-3) during clean northerly winds. Nocturnal metal concentrations more than doubled at T0, as pollutants became trapped in the nightly inversion layer, but decreased at the rural site. Transient spikes in concentrations of different metals, e.g. a "copper event" at T0 (CuPM10 281 ng m(-3)) and "zinc event" at T1 (ZnPM10 1481 ng m(-3)) on the night of March 7-8, demonstrate how industrial pollution sources produce localised chemical inhomogeneities in the city atmosphere. Most metal aerosols are <2.5 microm and SEM study demonstrates the dominance of Fe, Ti, Ba, Cu, Pb and Zn (and lesser Sn, Mo, Sb, W, Ni, V, As, Bi) in metalliferous particles that have shapes including spherical condensates, efflorescent CuZnClS particles, cindery Zn, and Cu wire. Metal aerosol concentrations do not change in concert with PM10 mass, which is more influenced by wind resuspension than industrial emissions. Metalliferous particles can induce cell damage, and PM composition is probably more important than PM mass, with respect to negative health effects, so that better monitoring and control of industrial emissions would likely produce significant improvements in air quality.

PM10 speciation and determination of air quality target levels. A case study in a highly industrialized area of Spain.

The paper shows how PM speciation studies allow the evaluation of the strategies to be followed to diminish PM pollution in highly industrialized areas with a large number of potential pollution sources. Evolution of levels and speciation of PM10 in the ceramic producing area of Castelló (East Spain) was studied from April 2002 until December 2005. PM10 levels were measured at one rural (Borriana-rural), two suburban (Almassora and Onda) and three urban (Borriana-urban, L'Alcora and Vila-real) sites, all influenced by the ceramics industry. Average PM10 levels varied between 27 and 36 microg/m3 for the study period. Evaluation of 1996-2005 PM data from Onda shows a clear decrease of PM levels since the beginning of 2002. Summer peak levels and winter minima occurred at both rural and suburban sites, whereas urban sites had no clear seasonal trend, with high PM10 episodes being due variously to local, regional, and African dust intrusion events. PM10 chemical analysis at four of the sites showed the dominant constituent to be mineral matter, exceeding by 5-12 microg/m3 the usual ranges of annual mineral loadings in PM10 at comparable Spanish urban or regional background sites with no industrial influence. Given current PM10 loadings, we recommend a lowering target of 3-5 microg/m3 of the annual mean at the urban sites, which should be achievable given available emission abatement techniques.

Superiority of activated charcoal alone compared with ipecac and activated charcoal in the treatment of acute toxic ingestions.

A prospective, randomized clinical trial compared the clinical effectiveness of syrup of ipecac and activated charcoal to that of activated charcoal alone in the treatment of acute toxic ingestions. Two hundred adult patients with mild to moderate oral overdoses were entered into the trial. Patients receiving only activated charcoal were discharged from the emergency department in significantly (P less than or equal to .05) less time than those receiving both syrup of ipecac and activated charcoal (6.0 +/- 0.3 vs 6.8 +/- 0.2 hours, respectively). The percentage of patients requiring nonpsychiatric hospitalizations was not significantly different between the two groups (11.2% vs 14.0%, respectively). For the hospitalized patients, the length of time spent in the ICU and in the hospital was not statistically different between the two groups. A complication rate of 5.4% was found with the ipecac and activated charcoal treatment compared with a 0.9% complication rate in the activated charcoal group (P less than or equal to .05). Three episodes of aspiration pneumonitis occurred after administration of ipecac and activated charcoal, while no episodes of aspiration were noted after treatment with only activated charcoal. Together, these data are consistent with the recommendation that ED treatment with activated charcoal alone be the gastrointestinal decontamination procedure of choice for the routine mildly-to-moderately orally poisoned adult patient.