Innovative methods for emission inventory development and evaluation: workshop summary

Emission inventories are an essential tool for evaluating, managing, and regulating air pollution. Refinements and innovations in instruments that measure air pollutants, models that calculate emissions, and techniques for data management and uncertainty assessment are needed to enhance emission inventories. This workshop provided recommendations for improving emission factors, improving emission models, and reducing inventory uncertainty. Communication that increases cooperation between developers and users of inventories is essential. Emission inventories that incorporate these improvements will meet the challenges of the future.     

Effects of ozone on foliar leaching in Norway spruce (Picea abies L. Karst): confounding factors due to NOx production during ozone generation

Previous experiments with conifers fumigated with O(3), produced by air-operated electric discharge ozonators, have provided evidence that O(3) increases the leaching of NO(3)(-), NH(4)(+), K(+), Ca(2+), Mg(2+) and some other cations from needles, when the trees are treated with acid mist. This evidence has provided the foundation of the ozone-acid mist hypothesis of spruce decline. We report experiments with Norway spruce saplings fumigated with purified and unpurified O(3). The results show that the accumulation of NO(3)(-) in the needles arises from the rapid deposition of N(2)O(5) and HNO(3) formed from N(2) in the ozonator. An increase in removal of NH(4)(+), Na(+), Ca(2+), Mg(2+), Zn(2+) and Mn(2+) from the needles during soaking in H(2)SO(4), pH3, was also observed, which was related to the increase in NO(3)(-) but was independent of O(3) concentration. It is concluded that results of previous experiments cited in support of the ozone-acid mist hypothesis arose from effects which were at least partly caused by N(2)O(5) produced as a contaminant, and were incorrectly attributed to ozone. Other effects, such as growth stimulations, visible symptons, enhanced frost sensitivity, and infestation by pests or pathogens, which have been attributed to O(3) generated by electric discharge in air, should be interpreted with caution. Future experiments with ozone must eliminate this problem by either using O(2)-driven ozonators, or by purifying the output from air-driven ozonators using cold and/or water traps.     

Background levels of non-ortho-substituted (coplanar) polychlorinated biphenyls in human serum of Missouri residents

This study characterizes the levels of polychlorinated biphenyls (PCB) congeners PCB 77, PCB 81, PCB 126, and PCB 169, in a group of 150 men and women with no documented exposure to PCBs. Its purpose is to provide current referent levels of coplanar PCBs in Missouri residents and to compare those levels to levels reported in the literature from the United States and other countries. Although this study used an extensive questionnaire assessing potential sources of exposure, no positive relations were found between these exposure sources and participants' PCB levels. The PCB levels for the four congeners measured were lower than any reported in the literature. PCBs 126 and 169 are only two of the dioxin-like congeners; however, their contribution makes up 11% of the total TEQ. Age was significantly related to PCB 126 and PCB 169. For every one-year increase in age, both PCB congeners increased by approximately 0.4 parts per trillion (ppt). There was no gender difference for PCB 126; however, PCB 169 levels were 3 ppt higher in males than females.     

Evaluation of an ecosystem model in ecological risk assessment of chemicals

We used a Lake Suwa version of Comprehensive Aquatic Systems Model (CASM_SUWA) to demonstrate the risk estimation of 10 different chemicals and examined the applicability and reliability of the model in ecological risk assessment by qualitatively and quantitatively comparing with the results of studies on multiple species using mesocosm tests. The qualitative comparison of the model results with those of the reported mesocosm tests indicated that some evidence observed in mesocosm studies supported the indirect effects predicted from simulation using the model. The comparison of the concentration levels at which 20% biomass reduction (BR20) in the most sensitive population estimated from the model with the no-observed effect concentration values derived from multiple species mesocosm tests (MS-NOEC) suggested that both data were related to each other and the model can be used to help in the determination of an ecological acceptable level of chemicals in aquatic environments. The analysis of the potential of indirect effects of a chemical for fish population indicated that the magnitude of the potential of indirect effects was quantified based on the ratio of BR50 to LC50 for fish population.     

Qualitative and quantitative cancer risk assessment of 2, 3, 7, 8-tetrachloro-dibenzo-p-dioxin (2, 3, 7, 8-TCDD)

The carcinogenicity of 2,3,7,8-TCDD at multiple organ sites in animals has been well established by several cancer bioassays. Results of two of the most notable of these, the Kociba et al. (1978) rat feeding study and the National Toxicology Program (1980) gavage study in rats and mice showed hepatocellular carcinomas in two strains of female rats and male and female mice. Other tumor sites included carcinomas of the lung, tongue, hard palate and nasal turbinates, thyroid, and subcutaneous tissue. The evidence for carcinogenicity of 2,3,7,8-TCDD in animals is regarded as “sufficient” using the classification system of the International Agency for Research on Cancer (IARC).

Two Swedish epidemiologic case-control studies (Hardell and Sandstrom, 1979; Eriksson et al. 1979, 1981) reported a significant five- to sevenfold excess risk of soft-tissue sarcomas (STS) from occupational exposure to chlorinated phenoxyacetic acid herbicides and/or chlorophenols. Additionally, several small cohort studies collectively exhibited an unusual cluster of STS, significantly increased over combined expected incidence. Problems with these studies do not appear to be sufficient to discount this excess risk. The human evidence alone for the carcinogenicity of 2,3,7,8-TCDD is “inadequate” using the IARC classification. However, for 2,3,7,8-TCDD in combination with chlorinated phenoxyacetic acid herbicides and/or chlorophenols, the human evidence is considered to be “limited.” The overall evidence for carcinogenicity considering both animal and human studies would place 2,3,7,8-TCDD alone in the IARC category 2B, meaning that the substance is probably carcinogenic in humans. The overall weight of evidence for 2,3,7,8-TCDD in combination with chlorinated phenoxyacetic acid herbicides and/or chlorophenols is regarded as IARC category 2A, also meaning that they are probably carcinogenic for humans.

Using current EPA methodology for quantitatively estimating cancer risks, several animal data sets have been analyzed. Comparing the results, the upper-limit incremental unit risk estimate is 1.6 × 10⁻² for a lifetime exposure of 1 ng/kg/day. This estimate is derived from a lifetime feeding study (Kociba et al., 1978) in which 2,3,7,8-TCDD induced tumors of the liver, lungs, hard palate, and nasal turbinates in female rats. Incremental unit cancer risks are also extrapolated for lifetime 2,3,7,8-TCDD exposures in water and air. Based on continuous lifetime exposure to 1 ng/L 2,3,7,8-TCDD in drinking water, the upper-limit estimate of extra cancer risk per individual is 4.5 × 10⁻³. For lifetime exposure to 1 pg 2,3,7,8-TCDD/m³ in the ambient air, the upper-limit individual risk is 3.3 × 10⁻⁵.     

Population History, Genetic Variability, and Horn Growth in Bighorn Sheep

Bighorn sheep ( Ovis canadensis ) are restricted in distribution and numbers relative to presettlement conditions. Some populations have alledgedly suffered losses of fitness resulting from small, insular populations and a breeding system that reduces effective population size. Large horns in rams, which confer breeding superiority, are absent from some populations, and this absence may result in part from loss of genetic variability. We investigated the relationship among allozyme variability, population history, and horn growth in bighorn sheep from the Rocky Mountains. Heterozygosity was higher for bighorn sheep than has been reported for Dall sheep ( O. dalli ). Heterozygosity and allelic variability were marginally related to effective population size for the proceeding 15 years. Horn growth was significantly higher in more heterozygous than in less heterozygous rams for years 6, 7, and 8 of life. By the end of year 8, more heterozygous rams had 13% higher horn volumes than less heterozygous rams. Most hunting of bighorn sheep involves selective removal of large-horned rams, which we hypothesize may reduce genetic variability of these populations and contribute to losses in fitness.     

The strategic use of innovation to influence regulatory standards

This paper investigates the welfare consequences of strategic behavior by firms to affect the amount of environmental regulation they face. Environmental regulation often attempts to force an industry to develop cleaner technology, but the regulator may have no means to commit to a specific standard. This lack of regulatory commitment induces firms to choose innovation strategically. It is well-known that firms have incentives to suppress innovation to induce the regulator to ratchet down the standard, and this strategic behavior lowers welfare. This paper explores a countervailing incentive. In oligopoly settings, firms have heightened incentives to innovate so as to increase regulation and raise rivals costs. In equilibrium, the incentive to raise rivals cost can mitigate the welfare loss arising from no regulatory commitment. Also, a regulator who is unable to commit ex ante to the stringency of a regulatory standard can induce more clean technology than a regulator with a commitment mechanism.     

The stability of trophic mass-balance models of marine ecosystems: a comparative analysis

Dynamic simulations of 18

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mass-balance marine trophic models are used to explore the stability of systems when briefly impacted by a fishery on the key ‘wasp–waist' populations occurring at intermediate trophic levels. The results are related to different ecosystem goal functions previously identified as representative of three attributes of ecosystems development: community complexity, homeostasis and energetics. System recovery time, the time required for all functional groups to returns to baseline level, and here used as a measure of model stability, was inversely correlated to Finn's Cycling Index, i.e. to the fraction of ecosystem throughput that is recycled, and to the mean length of trophic pathways in the systems. Systems with higher capacity to recycle detritus are systems with a higher ability to recover from perturbations. The results are in agreement with the E.P. Odum's theory of ecosystem development, where recycling is interpreted as a chief positive feedback mechanism that contributes to stability in the mature systems by preventing overshoots and destructive oscillations due to external impacts.     

Variable sex ratio among colonies of ants

Summary Small colonies of ants often produce mostly male alates, while large colonies produce mostly female alates. I present a simple model consistent with this pattern in which males that compete for mates are related (Local Mate Competition). The model explains the observed trend even when relatedness among competing males is low, so that there is only a negligible effect on the predicted sex allocation ratio in the population. The reverse trend is expected when there is competition among related females for a limited resource, such as nest sites (Local Resource Competition); small broods are predicted to be mostly female and large broods are predicted to be mostly male.