Accidental release of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at Sèveso, Italy. VI. TCDD levels in atmospheric particles

Assessment of dioxin-like soil contamination in Mexico by enzyme-linked immunosorbent assay

In this work, we describe the results of a preliminary soil assessment program for the detection of dioxins at different sites in Mexico performed by immunoassay. We studied five different sectors considered relevant sources of dioxins: Anaversa and Tekchem industrial areas where organochlorine pesticides were manufactured and released by accidental explosions, secondary smelters, brick kilns, and rural dwellings. In the context of the Agency for Toxic Substances and Disease Registry (ATSDR) guidelines, only the brick kilns sites can be considered as low-risk areas. The dioxin concentrations detected in the vicinity of the Anaversa and Tekchem chemical plants and secondary smelters exceed the screening level of 0.05 ppb set by the ATSDR, and therefore further site-specific studies are needed. The dioxin levels found in all soot samples from indigenous dwellings where wood is used for indoor cooking were above the evaluation level. Considering that the studied areas are representative examples of dioxin sources in less developed countries, our work demonstrates the useful application of dioxin immunoassays as a tool for dioxin screening for environmental assessment programs in developing countries.

Neonatal thyroid function in Seveso 25 years after maternal exposure to dioxin

BACKGROUND

Neonatal hypothyroidism has been associated in animal models with maternal exposure to several environmental contaminants; however, evidence for such an association in humans is inconsistent. We evaluated whether maternal exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a persistent and widespread toxic environmental contaminant, is associated with modified neonatal thyroid function in a large, highly exposed population in Seveso, Italy.

METHODS AND FINDINGS

Between 1994 and 2005, in individuals exposed to TCDD after the 1976 Seveso accident we conducted: (i) a residence-based population study on 1,014 children born to the 1,772 women of reproductive age in the most contaminated zones (A, very high contamination; B, high contamination), and 1,772 age-matched women from the surrounding noncontaminated area (reference); (ii) a biomarker study on 51 mother-child pairs for whom recent maternal plasma dioxin measurements were available. Neonatal blood thyroid-stimulating hormone (b-TSH) was measured on all children. We performed crude and multivariate analyses adjusting for gender, birth weight, birth order, maternal age, hospital, and type of delivery. Mean neonatal b-TSH was 0.98 microU/ml (95% confidence interval [CI] 0.90-1.08) in the reference area (n = 533), 1.35 microU/ml (95% CI 1.22-1.49) in zone B (n = 425), and 1.66 microU/ml (95% CI 1.19-2.31) in zone A (n = 56) (p < 0.001). The proportion of children with b-TSH > 5 microU/ml was 2.8% in the reference area, 4.9% in zone B, and 16.1% in zone A (p < 0.001). Neonatal b-TSH was correlated with current maternal plasma TCDD (n = 51, beta = 0.47, p < 0.001) and plasma toxic equivalents of coplanar dioxin-like compounds (n = 51, beta = 0.45, p = 0.005).

CONCLUSIONS

Our data indicate that environmental contaminants such as dioxins have a long-lasting capability to modify neonatal thyroid function after the initial exposure.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) in the environment: human health risk estimation and its application to the Seveso case as an example

Findings from selected dose-response experimental studies on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) carcinogenic action in rodents were utilized for low-dose lifetime cancer risk estimation in man. The Weibull, Armitage-Doll, and linearized Armitage-Doll mathematical models were employed in this work. Conversion factors, based on body surface, of 1/5 and 1/11 were also employed for rat- and mouse-to-man extrapolation. Conservative estimates from the linearized Armitage-Doll upper 99% confidence limit associate a 10(-5) risk probability level to TCDD daily doses of 0.15-2.4 pg/kg body wt., while levels of 10(-6) and 10(-7) are associated with uptakes 10- and 100-fold lower, respectively. Based on environmental microanalytical records, exposure to TCDD of Seveso (Milan, Italy) Zone B and R inhabitants was calculated from 0.5 year after the accident onward. Exposure through food produced locally was assumed to be zero. The lifetime cancer risk for the considered cohort at the highest exposure does not appear to exceed 10(-5).

Cutaneous signs of systemic toxicity due to dioxins and related chemicals

The controversy about dioxin effects on human health received a great deal of attention recently when the State of Missouri was declared to have a dioxin crisis. However, dioxin and several related chemicals are widespread throughout the world. Cutaneous signs play an important part in evaluating toxicity of dioxin and similar chemicals. Chloracne is the most sensitive indicator of significant dioxin exposure. Porphyria cutanea tarda and hyperpigmentation are other known cutaneous effects, and malignant fibrous histiocytomas of the skin may possibly be associated, although data are inconclusive on this point. The AMC Council on Scientific Affairs recommended that all physicians become familiar with chloracne and other toxic effects of dioxin. Dermatologists, especially, should be aware of the problem and may discover early cases of previously unsuspected exposure to this group of chemicals.

Health implications of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) contamination of residential soil

Extrapolations from animal toxicity experiments (including carcinogenicity and reproductive effects) to possible human heath effects can be used to estimate a reasonable level of risk for 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). Extrapolations are derived from: (1) review of published studies, (2) a complex set of assumptions related to human exposure to contaminated soil, and (3) estimates of (a) a dose response curve, (b) appropriate margins of safety, and/or (c) applicable mechanisms of action. One ppb of 2,3,7,8-TCDD in soil is a reasonable level at which to begin consideration of action to limit human exposure for contaminated soil.