Human health improvement in Sub-Saharan Africa through integrated management of arthropod transmitted diseases and natural resources.

A concept of an ecosystem approach to human health improvement in Sub-Saharan Africa is presented here. Three factors mainly affect the physical condition of the human body: the abiotic environment, vector-transmitted diseases, and natural resources. Our concept relies on ecological principles embedded in a social context and identifies three sets of subsystems for study and management: human disease subsystems, natural resource subsystems, and decision-support subsystems. To control human diseases and to secure food from resource subsystems including livestock or crops, integrated preventive approaches are preferred over exclusively curative and sectorial approaches. Environmental sustainability - the basis for managing matter and water flows - contributes to a healthy human environment and constitutes the basis for social sustainability. For planning and implementation of the human health improvement scheme, participatory decision-support subsystems adapted to the local conditions need to be designed through institutional arrangements. The applicability of this scheme is demonstrated in urban and rural Ethiopia.

Ecosystem health and human well being: the mission of the international programme on plant bioassays.

In a broad sense, since humans are ultimately a part of the ecosystem, we may conclude that ecosystem health encompasses human health. A preventative measure that detects the environmental hazards that infringe on human health should be established on a global scale. Plant bioassays, which are most sensitive in detecting genotoxicity of environmental agents, can serve as the first alert for the presence of environmental hazards in water, air, and soil-the essential elements of life. Three plant bioassays including the Allium/Vicia root test, the Tradescantia-Stamen-Hair-Mutation and Tradescantia-Micronucleus tests, which have been validated by the International Programme on Chemical Safety (IPCS), were selected to serve this purpose. The major activity of the International Programme on Plant Bioassays (IPPB) which was formerly sponsored by the IPCS has been devoted to the monitoring and testing of the genotoxicity of environmental pollutants using these three bioassays since 1996 after the hands-on workshop conducted in Qingdao, China. The general aim of this programme was not only to identify the substance and situations that may entail a significant risk to humans as proposed by ICPEMC and IAEMS but also by using these single, quick, and inexpensive plant bioassays to demonstrate the effects of pollution and to carry on environmental education to the general public at an early age. The monitoring network in China could be used as the model for a global scale study to aid in restoring ecosystem health. The Chinese policy is to identify the hazards and to eliminate the sources of pollution.

IPCS harmonization of methods for the prediction and quantification of human carcinogenic/mutagenic hazard, and for indicating the probable mechanism of action of carcinogens.

A flow chart is presented as a recommended sequence of tests to predict the carcinogenic hazard, and to predict and quantify the mutagenic hazard to germ cells of chemicals to humans. Ten associated principles of testing for these endpoints are also suggested. These recommendations are the result of a meeting convened under the auspices of the International Programme on Chemical Safety (IPCS), as part of their project on 'Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals'. The meeting was held at Carshalton, Surrey, from 13-17 February 1995.

Environmental monitoring for genotoxicity with plant systems. An introduction and study design.

Under the sponsorship of the International Programme on Chemical Safety (IPCS), 17 laboratories from diverse regions of the world participated in evaluating the utility of four plant bioassays for detecting genetic hazards of environmental chemicals. The bioassays included in this collaborative study were: Arabidopsis thaliana embryo and chlorophyll assay and Tradescantia stamen hair assay, Tradescantia paludosa micronucleus assay and Vicia faba root tip assay. Four to six laboratories participated in the performance of each of the bioassays. All laboratories participating in a particular bioassay were supplied with uniform plant material as well as standardized protocol. Five direct acting water soluble test chemicals, i.e. maleic hydrazide, methyl nitrosourea, ethyl methanesulfonate, sodium azide and azidoglycerol, were selected for this study. The study was designed to be completed in three phases. Ethyl methanesulfonate was used as a positive control and has already been reported earlier (Sandhu et al., 1991). The data from the remaining four chemicals used for the evaluation of four plant test systems in the first phase of the collaborative study are reported in this issue.

Environmental monitoring for genotoxicity with plant systems. Results and recommendations.

In the first phase of a collaborative study by the International Programme on Chemical Safety (IPCS), four coded chemicals, i.e. azidoglycerol (AG, 3-azido-1,2-propanediol), methyl nitrosourea (MNU), sodium azide (NaN3) and maleic hydrazide (MH), and ethyl methanesulfonate (EMS) as a positive control were tested in four plant bioassays, namely the Arabidopsis embryo and chlorophyll mutation assay, the Tradescantia stamen hair assay (Trad-SH assay), the Tradescantia micronucleus assay (Trad-MCN), and the Vicia faba root tip assay. Seventeen laboratories from diverse regions of the world participated with four to six laboratories each using one plant assay. For the Arabidopsis assay, laboratories were in agreement with MNU and AG giving positive responses and NaN3 giving a negative response. With the exception of one laboratory which reported MH as weakly mutagenic, no mutagenic response was reported for MH by the other laboratories. For the Vicia faba assay, all laboratories reported a positive response for MNU, AG, and MH, whereas two of the six laboratories reported a negative response for NaN3. For the Trad-SH assay, MH was reported as giving a positive response and a positive response was also observed for MNU with the exception of one laboratory. NaN3, which exhibited a relatively high degree of toxicity, elicited a positive response in three of the five laboratories. AG was found positive in only one of the two laboratories which tested this chemical. For the Trad-MCN assay, MNU and MH were reported as positive by all laboratories, while four out of five laboratories reported NaN3 to be positive. Only one of three laboratories reported AG to be positive. The major sources of variability were identified and considered to be in the same range as found in similar studies on other test systems. Recommendations were made for minor changes in methodology and for initiating the second phase of this study.

Cytogenetic effects of the food preservatives--sodium benzoate and sodium sulphite on Vicia faba root meristems.

Sodium sulphite and sodium benzoate induce in Vicia faba root meristems: (1) dose-dependent reduction in mitotic figures, (2) intact and severed anaphase bridges, (3) premature chromosome condensation heading to pycnotic nuclei, and (4) chromatin erosion in interphase nuclei. The effects are due to the anions and not due to the sodium ions. Complete recovery of mitotic figures and normal chromosome configurations were observed within the first 23-46 h of regrowth. Recovery was accompanied by severed anaphase bridges and micronuclei of various shapes. Both benzoate and sulphite inhibit DNA synthesis in Vicia faba root meristems. Sulphite was more effective than benzoate.

DNA and its precursors might interact with the food preservatives, sodium sulphite and sodium benzoate.

The interaction of sodium sulphite and sodium benzoate with nucleosides and DNA has been studied in vitro. Reduction in UV-absorbance was consistently noticed. However, no new products result from such interaction. It is likely that our previous observations of the effects of the 2 food preservatives on DNA synthesis and mitotis in Vicia faba root meristems is not due to direct action of the chemicals at the level of genetic material.

Inhibition by tryptophan of nucleolar RNA synthesis in salivary gland nuclei of Chironomus thummi.

Tryptophan, but not glutamine and lysine, inhibits the incorporation of 3H-uridine into nucleoli of explanted salivary glands by about 60%. In isolated nuclei also, the nucleolar incorporation of 3H-uridine triphosphate is reduced to about 50% by tryptophan. It is concluded that tryptophan acts directly at the nuclear level and the possible mechanisms.