Holly A. Hattemer-Frey

Benzo-a-Pyrene: Environmental Partitioning and Human Exposure

A multimedia transport model was used to evaluate the environ mental partitioning of benzo-a-pyrene (BaP). Measured and pre dicted environmental concentrations were used to estimate the accumulation of BaP in the food chain and the subsequent ex tent of human exposure from inhalation and ingestion. Results show that BaP partitions mainly into soil (82%) and sediment (17%) and that the food chain is the dominant pathway of hu man exposure, accounting for about 97% of the total daily in take of BaP. Inhalation and consumption of contaminated water are only minor pathways of human exposure. The long-term av erage daily intake of BaP by the general population of the U. S. is estimated to be 2.2 micrograms (μg) per day. Cigarette smok ing and indoor activities do not substantially increase human ex posure to BaP relative to exposures to background levels of BaP present in the environment. Since the increased lifetime risk as sociated with human exposure to background levels of BaP is 3.5 x 10 -4, we conclude that ingestion of food items contami nated with BaP may pose a serious health threat to the U. S. population.

Human exposure to dioxin

Because 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most potent chemical carcinogen evaluated by the U.S. Environmental Protection Agency (EPA), many people fear that exposure to even small amounts of TCDD could lead to serious health effects. Ambient measurements confirm that environmental TCDD contamination is widespread. The public is concerned about TCDD exposure from such diverse sources as municipal solid waste incinerators, pulp and paper mills, and contaminated fish and soil. This paper evaluates several critical issues including: (i) the extent of background contamination; (ii) accumulation in the food chain and the potential for human exposure from ingesting contaminated food items; (iii) the magnitude of TCDD emissions into the U.S. environment, and the relative contribution of various known TCDD sources to the total TCDD load; and (iv) setting environmental standards for TCDD.

Human exposure to 2,3,7,8-TCDD

Abstract This paper uses an environmental partitioning model to evaluate the concentration of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in various environmental media. These concentrations are then used to estimate the amount of TCDD entering the food chain and the average daily intake of TCDD by the general population of the US. The food chain accounts for 98% of human exposure to TCDD. The model estimated the average daily intake of TCDD to be 0.05 ng/day.

Pentachlorophenol: Environmental partitioning and human exposure

This paper uses a six compartment environmental partitioning model to explore the transport and accumulation of pentachlorophenol (PCP) within and between various environmental media. Environmental concentrations were then used to estimate the amount of PCP entering the food chain and the long-term, average daily intake of PCP by the general population of the U.S. Results show that PCP partitions mainly into soil (96.5%) and that the food chain, especially fruits, vegetables, and grains, accounts for 99.9% of human exposure to PCP. The long-term, average daily intake of PCP is estimated to be 16 μg/day, which agrees well with a previous estimate of 19 μg/day (Geyeret al. 1987).

Uptake of organics by aerial plant parts: A call for research

Abstract The purpose of this paper is to call for additional research on the uptake of organics by aerial plant parts. We establish two preliminary correlations for predicting the air-to-vegetation transfer of organic chemicals. Given the limited data data, however, it is impossible to conclude which relationship is more accurate. Regardless, the correlations demonstrate the potential importance of considering foliar uptake of organic chemicals as a source of vegetative contamination and subsequent human exposure.

Benzene: Environmental partitioning and human exposure

A multimedia transport model was used to evaluate the environmental partitioning of benzene. Measured and predicted environmental concentrations were used to estimate the accumulation of benzene in the food chain and the subsequent extent of human exposure from inhalation and ingestion. Results show that benzene partitions mainly into air (99.9%) and that inhalation is the dominant pathway of human exposure, accounting for more than 99% of the total daily intake of benzene. Ingestion of contaminated food items represents only a minor pathway of human exposure. The long-term average daily intake of benzene by the general population of the U.S. was estimated using three independent methods. Intake estimates based on measured personal air exposures, measured exhaled air concentrations, and a pharmacokinetically derived adipose tissue concentration (73, 63, and 72 micrograms/day, respectively) are in good agreement. Although inhalation is the primary route of human exposure to background levels of benzene in the environment, smoking was found to be the largest anthropogenic source of background human exposure to benzene.

Relationship between dietary intake of organic chemicals and their concentrations in human adipose tissue and breast milk

Octanol-water partition coefficients have been correlated with the bioaccumulation of organic chemicals in biological systems. It is demonstrated that the bioaccumulation of organics in human tissues was positively correlated with their octanol-water partition coefficients. The regression equations depicting this relationship were used to estimate the extent of past human exposure for the general population of the U.S. to organics for which measured background tissue concentrations are available. This technique provides an additional tool for evaluating the nature and extent of human exposure to environmental contaminants.

Comparison of human exposure to dioxin from municipal waste incineration and background environmental contamination

Abstract This paper characterizes the pathways and extent of human exposure to dioxin. The long-term, average daily intake of dioxin is estimated to be 0.05 ng/day. Results show that the food chain is the major source of human exposure to dioxin, while municipal waste incineration is not a principal source of human exposure.

Determining an acceptable level of risk

Past regulatory decisions explicitly acknowledge that some risks (i.e., risks in the range of 10/sup -6/ to 10/sup -3/) are acceptable in modern society. Regulatory agencies have an obligation to limit human exposure to chemical carcinogens to levels that are both acceptable and as low as reasonably achievable. However, the view that all risks greater than 10/sup -6/ are unacceptable and should be regulated no matter what the cost is economically unrealistic and is not compatible with past regulatory practice. Although it may seem barbaric to argue that some risks are acceptable and therefore must be endured by society, past regulatory decisions indicate that in many circumstances risks greater than 10/sup -4/ are in fact tolerated.

Small-scale field test of the genetically engineered lacZY marker☆

Commercial genetic engineering is advancing into areas that require the small-scale introduction of genetically engineered microorganisms (GEMs) to better quantify variables that affect microorganism distribution and survival and to document potential long-term consequences. A recombinant DNA marker system, the lacZY marker, developed by the Monsanto Agricultural Co., enables the distribution and fate of marked fluorescent pseudomonad organisms to be monitored under actual field conditions. Critical evaluation of GEMs under field conditions is imperative if plant-beneficial effects are to be correlated with organism release. This paper evaluates the effectiveness of this marker system and its ability to facilitate the assessment of risks associated with deliberate environmental introductions of genetically engineered microorganisms. Results of prerelease contained growth chamber and field experiments demonstrated that: (1) the scientific risk assessment methodology adopted by Monsanto and approved by the U.S. Environmental Protection Agency was appropriate and comprehensive; (2) the deliberate introduction of a GEM did not pose unacceptable or unforeseen risks to human health or the environment; (3) the lacZY marker is an effective environmental tracking tool; and (4) regulatory oversight should reflect the expected risk and not be excessively burdensome for all GEMs.