An approach for the assessment of risk from chronic radiation to populations of phytoplankton and zooplankton.

A conceptual model of the effects of chronic radiation on a population of phytoplankton and zooplankton in an oceanic nutrient layer is presented. The model shows that there are distinct threshold dose rates at which the different plankton populations become unsustainable. These are 10,400 microGy h(-1) for phytoplankton and 125 microGy h(-1) for zooplankton. Both these values are considerably greater than the current screening values for protection of 10 microGy h(-1). The model highlights the effects of predator-prey dynamics in predicting that when the zooplankton is affected by the radiation dose, the phytoplankton population can increase. In addition, the model was altered to replicate the dose rates to the plankton of a previous ERICA Irish Sea assessment (24 microGy h(-1) for zooplankton and 430 microGy h(-1) to phytoplankton). The results showed only a 10% decrease in the zooplankton population and a 15% increase in the phytoplankton population. Therefore, at this level of dose, the model predicts that although the dose rate exceeds the guideline value, populations are not significantly affected. This result highlights the limitations of a single screening value for different groups of organisms.

An approach to the assessment of risk from chronic radiation to populations of European lobster, Homarus gammarus (L.).

The basic principles underlying a four-discrete age group, logistic, growth model for the European lobster Homarus gammarus are presented and discussed at proof-of-concept level. The model considers reproduction, removal by predation, natural death, fishing, radiation and migration. Non-stochastic effects of chronic low linear energy transfer (LET) radiation are modelled with emphasis on (99)Tc, using three endpoints: repairable radiation damage, impairment of reproductive ability and, at higher dose rates, mortality. An allometric approach for the calculation of LD(50/30) as a function of the mass of each life stage is used in model calibration. The model predicts that at a dose rate of 1 Gy day(-1), lobster population reproduction and survival become severely compromised, leading eventually to population extinction. At 0.01 Gy day(-1), the survival rate of an isolated population is reduced by 10%, mainly through loss of fecundity, comparable to natural migration losses. Fishing is the main ecological stress and only dose rates in the range 0.03-0.1 Gy day(-1) can achieve discernible effects above it. On the balance of radiation and other ecological stresses, a benchmark value of 0.01 Gy day(-1) is proposed for the protection of lobster populations. This value appears consistent with available information on radiation effects in wildlife.

The effect of phosphate content on the bioactivity of soda-lime-phosphosilicate glasses.

We report on the bioactivity of two series of glasses in the SiO(2)-Na(2)O-CaO-P(2)O(5) system after immersion in simulated body fluid (SBF) after 21 days. The effect of P(2)O(5) content was examined for compositions containing 0-9.25 mol.% phosphate. Both series of glasses degraded to basic pH, but the solutions tended towards to neutrality with increasing phosphate content; a result of the acidic phosphate buffering the effect of the alkali metal and alkaline earth ions on degradation. Bioactivity was assessed by the appearance of features in the X-ray diffraction (XRD) traces and Fourier transform infrared (FTIR) spectra consistent with crystalline hydroxyl-carbonate-apatite (HCAp): such as the appearance of the (002) Bragg reflection in XRD and splitting of the P-O stretching vibration around 550 cm(-1) in the FTIR respectively. All glasses formed HCAp in SBF over the time periods studied and the time for formation of this crystalline phase occurred more rapidly in both series as the phosphate contents were increased. For P(2)O(5) content >3 mol.% both series exhibited highly crystalline apatite by 16 h immersion in SBF. This indicates that in the compositions studied, phosphate content is more important for bioactivity than network connectivity (NC) of the silicate phase and compositions showing rapid apatite formation are presented, superior to 45S5 Bioglass which was tested under identical conditions for comparison.

Dynamic model for the assessment of radiological exposure to marine biota.

A generic approach has been developed to simulate dynamically the uptake and turnover of radionuclides by marine biota. The approach incorporates a three-compartment biokinetic model based on first order linear kinetics, with interchange rates between the organism and its surrounding environment. Model rate constants are deduced as a function of known parameters: biological half-lives of elimination, concentration factors and a sample point of the retention curve, allowing for the representation of multi-component release. The new methodology has been tested and validated in respect of non-dynamic assessment models developed for regulatory purposes. The approach has also been successfully tested against research dynamic models developed to represent the uptake of technetium and radioiodine by lobsters and winkles. Assessments conducted on two realistic test scenarios demonstrated the importance of simulating time-dependency for ecosystems in which environmental levels of radionuclides are not in equilibrium.

Uptake and depuration of 131I from labelled diatoms (Skeletonema costatum) to the edible periwinkle (Littorina littorea).

Uptake and depuration of (131)I into winkles through consumption of the diatom Skeletonema costatum is described. The work follows on from previous studies that investigated the uptake of iodine into winkles from seawater and seaweed. Incorporation of (131)I in S. costatum from labelled seawater followed linear first-order kinetics with an uptake half-time of 0.40 days. Iodine uptake in winkles from labelled S. costatum also followed linear first-order kinetics, with a calculated equilibrium concentration (C(infinity)) of 42Bqkg(-1) and a transfer factor (TF) of 1.1x10(-4) with respect to labelled diatom food. This TF is lower than that observed for uptake of (131)I in winkles from labelled seaweed. For the depuration stage, a biphasic sequence with biological half-lives of 1.3 and 255 days was determined. The first phase is biokinetically important, given that winkles can lose two-thirds of their activity during that period. This study shows that, whilst winkles can obtain radioactive iodine from phytoplankton consumption, they do not retain the majority of that activity for very long. Hence, compared with other exposure pathways, such as uptake from seawater and macroalgae, incorporation from phytoplankton is a relatively minor exposure route.

Human behaviour and the transmission of dracunculiasis: a case study from the Ilorin area of Nigeria.

Dracunculiasis, infection with guinea worm, Dracunculus medinensis, is a debilitating disease causing considerable human misery and having an adverse impact on food production in affected areas. It can be entirely eradicated by the provision of protected drinking water for all members of the community. There are two phases in the transmission cycle associated with human activities, swallowing the infective guinea worm larvae in infected water and, 10-12 months later, the immersion of a limb with a guinea worm lesion on it in a drinking water source. In planning control strategies it is essential to understand the patterns of behaviour associated with these two phases of transmission. These include water consumption, water use and water treatment, patterns of water collection and population mobility. The recent increase in the levels, frequency and distance involved in population circulation is associated with increased prevalence rates. This analytical framework is used in a study of disease transmission in the area within a 50 kilometer radius of Ilorin, the capital of Kwara State, Nigeria. The conclusion briefly suggests some benefits which might accrue to affected areas as the result of the consideration of behavioural factors involved in disease transmission.

The distribution of dracunculiasis in Nigeria: a preliminary study.

This paper presents a preliminary assessment of the distribution and endemicity of dracunculiasis in Nigeria. The disease is found in all 19 States of the Federation and in the Federal Capital Territory of Abuja. It occurs in areas with a dry season of more than nine months as well as those with a dry season of less than four months; the seasonal distribution of rainfall influences the peak period of disease transmission and patency. Altogether, an estimated 2.5 million cases occur every year, and at least 30% of the entire rural population is at risk from the infection. The widespread distribution of dracunculiasis throughout the country indicates the need for a national control campaign and a sustained programme of international cooperation.

Dracunculiasis in Africa in 1986: its geographic extent, incidence, and at-risk population.

This paper presents a preliminary assessment of the geographic extent and estimates of the incidence and the population at risk of dracunculiasis in Africa. Nineteen countries are known to be affected, in a belt extending right across the northern part of the continent south of 18 degrees N, and in east Africa extending almost to the equator. Annual incidence is estimated to be 3.32 million, and the at-risk population is approximately 120 million. These data provide an initial baseline on which the success of control measures now being initiated in Africa can be assessed.

The impact of a UNICEF-assisted rural water project on the prevalence of guinea worm disease in Asa, Kwara State, Nigeria.

This paper demonstrates that protected water supplies, in the form of boreholes, can reduce the prevalence of dracunculiasis (guinea worm disease) in affected communities from a point prevalence of greater than or equal to 50% to 0% or near 0% within 3 years of intervention. Studies in Nigeria show that boreholes sited within a village and used exclusively for drinking water are most effective, while less accessible or malfunctioning boreholes have a less dramatic impact on prevalence. In contrast to the situation in villages served with boreholes, the prevalence of guinea worm in the unserved villages remained almost unchanged. The rapid benefits of protected rural water supplies and the decline of dracunculiasis, including the rise in school enrollment and fall in the rate of school absenteeism, are highlighted together with other socioeconomic benefits.

A charged-particle microbeam: II. A single-particle micro-collimation and detection system.

The use of a charged-particle microbeam provides a unique opportunity to control precisely, the number of particles traversing individual cells and the localization of dose within the cell. The accuracy of 'aiming' and of delivering a precise number of particles crucially depends on the design and implementation of the collimation and detection system. This report describes the methods available for collimating and detecting energetic particles in the context of a radiobiological microbeam. The arrangement developed at the Gray Laboratory uses either a 'V'-groove or a thick-walled glass capillary to achieve 2-5 microns spatial resolution. The particle detection system uses an 18 microns thick transmission scintillator and photomultiplier tube to detect particles with > 99% efficiency.

The comparative study of patterns of guinea worm prevalence as a guide to control strategies.

Guinea worm, a parasite found in unprotected drinking water sources, causes considerable morbidity and loss of agricultural production among rural people in India and West Africa. A comparative study of village level prevalence data in the two regions reveals marked contrasts in the level and characteristics of prevalence which are useful guidelines in planning control strategies where little is known about local guinea worm epidemiology. Prevalence rates of up to 75-80% of the total population of a settlement have been found in West Africa, far higher than those in India. The higher figure indicates that all members of a community are exposed to a common infected drinking water source. Here the infection affects all sections of the population who do not treat their water at the household level. In India levels of prevalence for males are far higher than for females, whereas in West Africa the difference in infection rates between the sexes is less marked. In India many men are infected when they are away from the village, attending festivals or farming, and exposed to untreated water sources; women and children travel less and use domestic water sources which are more likely to be treated in some way. Differences in prevalence characteristics according to age, sex or social/economic grouping should be taken into account when planning national and local control campaigns. For example, in Nigeria where women are as likely to suffer from the infection as men, women are the main water collectors and contaminators, and are responsible for domestic water treatment; thus they should be fully involved in control campaigns.(ABSTRACT TRUNCATED AT 250 WORDS)

Population mobility and disease transmission: the example of guinea worm.

Population mobility can bring people into contact with disease agents, and transfer these agents to new populations. This paper suggests ways in which population movements are implicated in the transmission of one communicable disease, guinea worm or dracunculiasis, a parasitic disease affecting 5-15 million people every year in Africa, India and Pakistan. A typology of population mobility which distinguishes between rural and urban sectors, and between circulation and uni-directional permanent migration is used. An understanding of population movements associated with guinea worm, and with other communicable diseases, can also provide useful guidelines for effective disease control strategies.

Child health and child care in Okelele: an indigenous area of the city of Ilorin, Nigeria.

This paper provides a detailed analysis of the survival rates and health problems of a cohort of children born during a 5-yr period in part of the city of Ilorin, Nigera. The findings are linked to a demographic and environmental study which indicates that the study area was relatively stable in terms of family structure and population turnover. Most people work in the informal sector, in trading, small scale crafts and service industries. At the time the survey began, in 1979, the provision of piped water supplies to the area was unreliable and sanitation provisions rudimentary. Most of the people had little or no formal education and were very poor. The study indicated that health status had improved over the 5-yr period, compared to a baseline study conducted in 1979. Common causes of child mortality and morbidity included diarrhea, acute respiratory infections, measles, and malaria. The infant mortality rate was 41.5/1000. The availability of clinic care at nominal cost, and the attendance of mothers at the clinic for checkups and immunization, resulted in a higher level of health for their children than otherwise would have been possible. Some problems of primary health care in the area are mentioned, in the light of Nigeria's current budgetary problems, and the utilization of existing strong social support networks to improve health care and environmental sanitation and water supply is suggested.

Guinea worm: an in-depth study of what happens to mothers, families and communities.

This paper reports on the impact of maternal morbidity due to guinea worm, dracunculiasis, on the care and health of children under 24 months old, and the way in which the mothers and the family coped with the often extended periods of disability. This qualitative study is based on observation and in-depth interviewing, supplemented by focus group discussions. Of 42 mothers with guinea worm in two hyperendemic areas of Oyo and Kwara States, 28 were either bedridden or only able to hobble short distances with the help of a stick; the average period of incapacity was almost 9 weeks. Of the four maternal roles identified (child care, self care, domestic tasks, income generation), the women gave priority to child care; 34 of the 42 mothers needed help in child care. Coping networks operated principally within the extended family, but also included women in other households, and women from beyond the community. Thus the impact of a mother's illness extended beyond her children and family to the wider community. This qualitative study thus reveals the multifaceted impact of a disease on individuals and on the community. The study stresses the need for, and availability of, effective methods for controlling guinea worm by utilizing community cooperation to provide protected water sources and other preventive measures against the disease.

A method of rapid assessment of the distribution and endemicity of dracunculiasis in Nigeria.

This paper describes how information was collected at a national conference in Nigeria and a map compiled to give an initial assessment of the distribution and endemicity of dracunculiasis (guinea worm disease) throughout the country. The map provided a stimulus for further studies of the status of the disease and for the consideration of national control strategies. A map created along the same lines could be used for obtaining an initial assessment of the extent and endemicity of dracunculiasis, or other diseases, in countries for which such data was not readily available.

Medialization of electrode array in cochlear implantation.

In the last few years, the main thrust of research into cochlear implantation has centred around the development of advanced multi-channel implants. A new area of development is now concentrating on maximizing the potential of each individual electrode in order to improve the quality of hearing. This study involved the medialization of the cochlear implant electrode array using a silastic positioner in five patients. Two parameters were measured, namely current units needed to produce a stapedial reflex, and impedance levels between the electrode and modiolus. On insertion of the cochlear implant, readings were taken before the insertion of the positioner, immediately afterwards and at two months.

Facial paralysis caused by a lymphoepithelial cyst located in the parotid gland.

We report the case of an acute onset facial paralysis which was caused by a benign lymphoepithelial cyst found in the parotid, an association which is a rarity in the literature. The diagnosis and surgical management is discussed. This report emphasises the clinical principle that parotid masses causing an acute facial palsy are not necessarily malignant in nature. Intra-operative frozen section histology is helpful in saving the patient from unnecessarily radical surgery.

Endemicity and striking manifestations of onchocerciasis in Shao, Kwara State, Nigeria.

A house-to-house screening exercise was carried out in Shao, Kwara State, Nigeria, to determine the status of onchocerciasis in the town. The results of skin snips taken from 2018 subjects revealed that, with an overall infection rate of 54.6%, the community is mesoendemic for river blindness. The prevalence and intensity of the infection were significantly higher for adults than for children, for males than for females and for farmers than for other occupational groups (P less than 0.01). The severity and frequency of occurrence of striking manifestations of onchocerciasis, including blindness, hernias, hanging groins, 'leopard skin' and scrotal elephantiasis, strongly suggest that the community had a history of long-standing onchocerciasis. The desirability for the implementation of a nation-wide control programme in Nigeria to complement the ongoing control efforts in the Volta River Basin Areas, is highlighted.