On the validity of classifying chemicals for persistence, bioaccumulation, toxicity, and potential for long-range transport

Mackay, D.; McCarty, L.S.; MacLeod, M.
2001 | Environ. Toxicol. Chem. | 20 (7) (1491-1498)

It is argued that chemical substances can be meaningfully ranked or classified according to their persistence (P), bioaccumulation (B), toxicity (T), and potential for long-range transport (LRT) only if these attributes can be shown to be intensive, as distinct from extensive, properties of the substance, i.e., they are independent of quantity of substance. It ii shown that P, B, and LRT can be considered intensive or quasi-intensive properties, but toxicity is more problematic. To obtain an intensive metric of toxicity requires selection of one of several possible extensive quantities that define exposure or dose. Ranking of a group of chemicals by toxicity is shown to be very dependent on which quantity is selected. It is suggested that toxicity metrics, such as lethal concentration to 50% of the population (LC50), lethal dose to 50% of the population (LD50), and threshold limit value (TLV) suffer the severe disadvantage of bring dependent on the efficiency of delivery of the substance to the site(s) of toxic action in the organism. The use of measured or calculated internal dose is a preferable measure of toxicity since it reduces ambiguities inherent in the other metrics. Also, the primary concern is not the quasi-intensive property of toxicity, rather. it is the risk of toxic effects, an extensive quantity. To adequately assess the risk of toxic effects, both the toxic hazard and the degree of exposure must be characterized. Since exposure cannot be estimated without knowledge of the emission rate of chemicals to the environment. a compelling case can be made that screening to identify priority P, B, T. and LRT substances should be expanded to include quantity released to the environment as an additional factor.

A modeling strategy for planning the virtual elimination of persistent toxic chemicals from the Great Lakes: An illustration of four contaminants in Lake Ontario

Thompson, S.; Mackay, D.; MacLeod, M.
1999 | J. Great Lakes Res. | 25 (4) (814-827)

A systematic seven-step process is proposed as a strategy for planning "virtual elimination" of persistent toxic contaminants in the Great Lakes. The strategy involves (i) estimating loadings (ii) gathering prevailing concentration data, (iii) obtaining physical-chemical property data for the chemicals of interest, (iv) obtaining data concerning conditions in the lake, (v) applying a relatively simple steady-state mass balance model incorporating an appropriate treatment of variability and uncertainty to reconcile the range of estimated concentrations with the range of monitoring data, (vi) identifying reasonable targets for loading reductions, and finally (vii) applying the model in dynamic form to estimate virtual elimination. The uncertainties in these estimates are quantified to convey an impression of their perceived accuracy. The strategy is illustrated for four contaminants (polychlorinated biphenyls, benzol(b)fluoranthene, arsenic, and lead) in Lake Ontario.

An assessment of the environmental fate and exposure of benzene and the chlorobenzenes in Canada

MacLeod, M.; Mackay, D.
1999 | Chemosphere | 38 (8) (1777-1796)

Systematic modelling of the fate of benzene and the chlorobenzenes is presented which follows a four-stage process of chemical classification, quantifying discharge rates and environmental concentrations, evaluative assessment of fate and regional mass balance modelling has been carried out for the southern Ontario region. The EQC model was applied to determine the principal transport and transformation processes experienced by this group of chemicals, which vary considerably in volatility and hydrophobicity. Observed environmental concentrations are in satisfactory agreement with the predictions of the steady state Level III ChemCAN model of chemical fate. A multiple pathway human exposure model which estimates intake of contaminants by residents of southern Ontario has been developed and applied to these chemicals. A novel method of deducing maximum tolerable environmental concentrations is presented. Results suggest that benzene and 1,4-dichlorobenzene are present in the environment at levels sufficient to cause exposures near allowable daily intake (ADI) levels for the general population, but the other substances are present at levels which result in exposure ranging from 1/10 to 1/1000 of the ADI. (C) 1999 Elsevier Science Ltd. All rights reserved.

Synthetic application of monoprotected hydrazines toward the synthesis of 1-aminopyrroles

MacLeod, M.; Boudreault, N.; Leblanc, Y.
1996 | J. Org. Chem. | 61 (3) (1180-1183)

Diurnal Variability of Persistent Organic Pollutants in the Atmosphere over the Remote Southern Atlantic Ocean

Rosalinda Gioia; Matthew MacLeod; Javier Castro-Jimenez; Luca Nizzetto; Jordi Dachs; Rainer Lohmann; Kevin C Jones
1970 | ATMOSPHERE | 5 (622-634)

Towards the next generation of air quality monitoring: Persistent organic pollutants (POPs)

Hung, H.; MacLeod, M.; Guardans, R.; Scheringer, M.; Barra, R.; Harner, T.; Zhang, G.
1970 | Atmos Environ | (in press)

Persistent Organic Pollutants (POPs) are global pollutants that can migrate over long distances and bioaccumulate through food webs, posing health risks to wildlife and humans. Multilateral environmental agreements, such as the Stockholm Convention on POPs, were enacted to identify POPs and establish the conditions to control their release, production and use. A Global Monitoring Plan was initiated under the Stockholm Convention calling for POP monitoring in air as a core medium; however long temporal trends (>10 years) of atmospheric POPs are only available at a few selected sites. Spatial coverage of air monitoring for POPs has recently significantly improved with the introduction and advancement of passive air samplers. Here, we review the status of air monitoring and modeling activities and note major uncertainties in data comparability, deficiencies of air monitoring and modeling in urban and alpine areas, and lack of emission inventories for most POPs. A vision for an internationally-integrated strategic monitoring plan is proposed which could provide consistent and comparable monitoring data for POPs supported and supplemented by global and regional transport models. Key recommendations include developing expertise in all aspects of air monitoring to ensure data comparability and consistency; partnering with existing air quality and meteorological networks to leverage synergies; facilitating data sharing with international data archives; and expanding spatial coverage with passive air samplers. Enhancing research on the stability of particle-bound chemicals is needed to assess exposure and deposition in urban areas, and to elucidate long-range transport. Conducting targeted measurement campaigns in specific source areas would enhance regional models which can be extrapolated to similar regions to estimate emissions. Ultimately, reverse-modeling combined with air measurements can be used to derive “emission” as an indicator to assess environmental performance with respect to POPs on the country, region, or global level.

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Geovetenskapens Hus,
Svante Arrhenius väg 8, Stockholm

Arrheniuslaboratoriet, Svante Arrhenius väg 16, Stockholm (Unit for Toxicological Chemistry)

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Department of Environmental Science
Stockholm University
106 91 Stockholm

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