Environmental risk evaluation of chemicals: achievements of the project and seeds for future--development of metrics for evaluating risks

Achievements of the research project entitled "Establishment of a scientific framework for the management of toxicity of chemicals based on environmental risk-benefit analysis" supported by the JST were introduced and reviewed, focusing on the development of the methodology for estimating risks; human health risks and ecological risks. The usefulness of loss of life expectancy as a metric for evaluating cancer and noncancer risks was demonstrated. To evaluate ecological risks, three metrics, 1/T, logT and T, developed based on the mean extinction time (T) of species were proposed. Then, their implication and feasibility were examined in terms of what ecological system should be conserved and how easily people can understand the implications of metrics. Protocols for estimating human health risks and ecological risks are illustrated.     

Screening of agonistic activities against four nuclear receptors in wastewater treatment plants in Japan using a yeast two-hybrid assay

To assess the potential endocrine disruptive effects through multiple nuclear receptors(NRs),especially non-steroidal NRs,in municipal wastewater,we examined the agonistic activities on four NRs(estrogen receptor α,thyroid hormone receptor α,retinoic acid receptor α and retinoid X receptor α) of untreated and treated wastewater from municipal wastewater treatment plants(WWTPs) in Japan using a yeast two-hybrid assay.Investigation of the influent and effluent of seven WWTPs revealed that agonistic activities...     

Vertical distributions of (99)Tc and the (99)Tc/(137)Cs activity ratio in the coastal water off Aomori, Japan

Using a sector-field ICP-MS the vertical distributions of the ⁹⁹Tc concentration and ⁹⁹Tc/¹³⁷Cs activity ratio were measured in the coastal waters off Aomori Prefecture, Japan, where a spent-nuclear-fuel reprocessing plant has begun test operation. The ⁹⁹Tc concentrations in surface water ranged from 1.8 to 2.4 mBq/m³, no greater than the estimated background level. Relatively high ⁹⁹Tc/¹³⁷Cs activity ratios (10-12 × 10⁻⁴) would be caused by the inflow of the high-⁹⁹Tc/¹³⁷Cs water mass from the Japan Sea. There is no observable contamination from the reprocessing plant in the investigated area. The ⁹⁹Tc concentration and the ⁹⁹Tc/¹³⁷Cs activity ratio in water column showed gradual decreases with depth. Our results implied that ⁹⁹Tc behaves in a more conservative manner than ¹³⁷Cs in marine environments.     

Neurologic features of chronic minamata disease (organic mercury poisoning) and incidence of complications with aging

Abstract

To elucidate the neurologic features of chronic Minamata disease, and the incidence of complications with aging, we studied 80 patients with documented Minamata disease (organic mercury poisoning) from 1986 to 1994 (mean age: 63 years). Of the cardinal neurologic findings, sensory impairment was seen with highest frequency in 98.8% of patients limited to the extremities in 86.3%. Impairment of lower extremity coordination was observed in 60%, constriction of the visual field in 51.9%, and retrocochlear hearing loss in 41%. To assess age‐related complications, patients were separated into three groups by age: Group I (10 to 39 years); Group II (40 to 69 years); Group III (≥7 0 years). The incidences of hypertension and cerebrovascular diseases, organic ophthalmologic disorders (including cataracts), presbyacusis, and cervical spondylosis deformans increased significantly with age. Compared with a preceding survey (1981 to 1985, 171 patients, mean age: 63.5 years), the incidences of complicated hypertension and cataracts had decreased, whereas those of cerebrovascular disease and retinitis pigmentosa remained unchanged. The incidences of abnormal brain computed tomography (CT), presbyacusis, cervical spondylosis deformans, and positive tests for urine sugar also increased. The incidences of these complications other than retinitis pigmentosa were similar to those in the general population. These results accurately reflect the recent epidemiological disease tendencies in Japan toward a decreased incidence of hypertension and an increased incidence of diabetes.     

Polychlorinated dibenzo-p-dioxins,dibenzofurans and polychlorinated biphenyls in polar bear,penguin and south polar skua

Concentrations of 2378-substituted polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (DFs) and non- and mono-ortho-substituted polychlorinated biphenyls (dioxin-like PCBs) were measured in livers of polar bears from the Alaskan Arctic and in eggs of Adelie penguin and south polar skua and weddell seal liver, fish and krill from Antarctica. This is one of the first reports to document the concentrations of PCDDs/DFs in polar bear livers from Alaska, and in penguin and skua eggs from Antarctica. Concentrations of total PCDD/DFs in livers of polar bears ranged from 8 to 66 (mean: 26) pg/g, on a lipid weight basis. Concentrations of total PCDD/DFs in Antarctic samples were in the increasing order on a lipid weight basis; weddell seal liver (8.9 pg/g) < fish (11-17 pg/g) < krill (27 pg/g) > penguin eggs (30 ng/g) > seal liver (57 ng/g) > fishes (6.2 ng/g) > krill (0.9 ng/g). Concentrations of 2378-tetrachlorodibenzo-p-dioxin equivalents (TEQs) calculated based on the WHO TEFs were higher in the eggs of polar skua (mean: 344: range: 220-650 pg/g, lipid wt.) from Antarctica than in polar bear livers from Alaska (mean: 120; range: 69-192 pg/g). In general, concentrations of PCDFs were greater than those of PCDDs in polar organisms. 23478-PeCDF is one of the dominant congener found in several samples. Concentrations of TEQs in polar bear livers and skua eggs were close to those that may cause adverse health effects. Dioxin-like PCBs, particularly, non-ortho coplanar PCBs were the major contributors to TEQ concentrations in penguin and skua eggs whereas mono-ortho PCBs accounted for a major portion of TEQs in polar bear livers.     

Extinction risk to bird populations caused by DDT exposure

The impact of toxic chemicals on wild animals and plants can be quantified in terms of the enhanced risk of population extinction. To illustrate a method for doing this, we estimated such impact for two bird species: herring gull (Larus argentatus) in Long Island, NY, and sparrowhawk (Accipiter nisus) in eastern England, when they were exposed to DDT (p,p(')-dichlorodiphenyltrichloroethane) and its metabolites (called DDTs). The method we used is based on a formula of the mean time to population extinction derived for a stochastic differential equation (the canonical model). The intrinsic rate of natural population growth was estimated from an exponentially growing population, and the intensity of the environmental fluctuation was estimated from the magnitude of population size fluctuation. The effect of exposure to DDTs in reducing the population growth rate was evaluated based on an age-structured population model, by assuming that age-specific fertility is density-dependent and sensitive to DDTs exposure, but age-specific survivorship is not. The results are expressed in terms of the risk equivalent--the decrease in carrying capacity K that causes the same enhancement of extinction risk as chemical exposure at a given level. The risk equivalent can be used in mitigation banking.     

Detailed study on the levels of polychlorinated dibenzo-p-dioxins,polychlorinated dibenzofurans and polychlorinated biphenyls in Yusho rice oil

One bottle of Yusho rice oil was obtained from a Yusho family in 1998. The levels of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in the causal oil were investigated with two different approaches and the individual concentrations of all the 17 2,3,7,8-substituted PCDD/F and 14 coplanar PCB (Co-PCB) congeners were elucidated for the first time. The concentrations of PCDDs and PCDFs were found to be 0.60 and 8.8 ppm, respectively. For PCBs, more than 130 PCB peaks were observed and a total concentration of 850 ppm including 170 ppm of Co-PCBs was obtained. The toxic equivalents (TEQs) of PCDDs, PCDFs, and Co-PCBs were calculated to be 17, 470, and 120 ppb, respectively. The relative contribution of these classes to the total TEQ in Yusho oil is 3%, 77%, and 20%, respectively, indicating that PCDFs play a major role in the toxicity of Yusho oil. Furthermore, it was confirmed that 2,3,4,7,8-penta-CDF contributes 58% to the total TEQ, supporting the view that this compound is the principal causal agent in Yusho poisoning. It is noteworthy that the most toxic 2,3,7,8-tetra-CDD was newly discovered, although it contributes only 0.1% to the total TEQ. Based on our data, the smallest TEQ intake during the latent period was estimated to be 0.067 mg for Yusho patients. This value is about 60% of that previously reported, suggesting a lower minimum threshold level for the development of the toxic symptoms of Yusho.     

Gasification of waste plastics by steam reforming in a fluidized bed

The process of producing synthetic gas from waste plastics by steam reforming was investigated. To evaluate this process, the steam reforming of the oils derived from low-density polyethylene and polystyrene were carried out using a laboratory-scale fluidized bed of Ni-Al₂O₃ catalysts. The performance of gasification in terms of carbon conversion, gas yield, and gas compositions was examined. Although oils derived from plastics contain many kinds of heavy hydrocarbons and aromatics, they were well gasified at temperatures above 1023 K with a steam/carbon ratio of 3.5 and a weight hourly space velocity of 1 h⁻¹. The hydrogen content of the product gas was very high at approximately 72 vol% for polyethylene-derived oil and 68 vol% for polystyrene-derived oil. These compositions agreed well with the values calculated from chemical equilibrium.     

Two-stage thermal gasification of polyolefins

Plastic pellets of polyethylene (PE), polypropylene (PP), and polystyrene (PS) were gasified in a two-stage thermal degradation process. The first stage is the conversion of polyolefins to distilled oils using a melting vessel. In the second stage, the oils from the first stage are gasified using a tubular reactor. The distilled oil yields of PE, PP, and PS in the first stage were 84, 89, 92 wt%, respectively, each at 470°C. The total gas yields of PE, PP, and PS in the second stage were 80, 74, and 6.2 wt%, respectively, each at 800°C. The main components of the product gas for PE and PP were methane and olefins such as ethene and propene. Some aromatic oils, including benzene, toluene, and xylene, were also produced as by-products. The amount of carbonaceous residue, or coke, was very low (less than 1 wt%). By dividing the process into two stages, the coking rate was considerably reduced compared with direct gasification of the polyolefins. Received: July 19, 2000 / Accepted: September 17, 2000     

Mercury pollution in the Tapajos River basin, Amazon: mercury level of head hair and health effects.

There is increasing concern about the potential neurotoxic effects of exposure to methylmercury for the 6 million people living in the Amazon, even in regions situated far away from the gold mines (garimpos), considered to be the major source of mercury pollution. In November 1998, a spot investigation on mercury contamination was conducted in three fishing villages (Barreiras, Rainha, and Sao Luiz do Tapajos) on the Tapajos River, an effluent of the Amazon, situated several hundred kilometers downstream from the gold-mining areas. A total of 132 fishermen and their families volunteered for the current study. As was anticipated, the total mercury levels in the head hair collected from the fishing villages were relatively high (14.1-20.8 ppm on the average) and the number of subjects with a high total mercury level over 10 ppm (the least upper bound of a normal value) was 103 (78.0%) in total, along with various symptoms, thereby suggesting wide mercury contamination in the Tapajos River basin. Moreover, in view of the absence of other diseases (e.g., alcoholism or malaria), a high intake of fish containing a methylmercury level, and high hair mercury levels in addition to the various symptoms such as sensory disturbance (especially glove-and-stocking type, which is characteristic of Minamata disease), tremor, failure in two-point discrimination, and slight balancing failure, several subjects examined were diagnosed with mild Minamata disease. The findings obtained suggest, thus, that the mercury pollution in the Amazon should be crucially observed for head hair mercury level and health in a much broader region.