Environmental risk assessment of releases of transgenic plants containing virus-derived inserts

Sequences derived from the genomes of plant viruses are being used to provide virus resistance in transgenic crop plants. Although the environmental hazards associated with the release of such plants have been discussed widely, it has not been possible to reach generally acceptable conclusions about their safety. A case-by-case approach to the risk assessment of real examples is recommended as a means of building up confidence and of indicating areas of uncertainty. A logical framework for risk assessment is suggested, a key feature of which is identification of the viruses in the release environment that may infect the transgenic plants. Each of these is considered in relation to each of the three main classes of hazard (transcapsidation, recombination and synergism), and the risk associated with each event is analysed.     

An Improved Method for Preparing the Chromosomes of Pines and other Gymnosperms

A simple technic is described to produce well spread gymnosperm chromosomes. Root tip meristems are digested with a pectinase:cellulase mixture to produce a cell suspension which then is squashed to yield flat, well spread chromosome complements that can be stained or used for in situ hybridization.     

Natural Occurrence ofChondrostereum purpureumin Relation to Its Use as a Biological Control Agent in Canadian Forests

The incidence of natural fructification ofChondrostereum purpureumwas estimated quantitatively on southern Vancouver Island during two winter seasons in randomly located 1000-m²plots and compared with potential added fructification that might occur as a result of using the fungus to control stump-sprouting of hardwood weeds in young forest stands. Fructification was surveyed in forests as well as in urban or agricultural areas by estimating the surface areas of woody substrates covered with basidiocarps. In addition to random plots, estimates were made also in locations where the fungus would be expected to occur (woodpiles, silvicultural thinnings, and killed trees). Basidiocarps were found throughout the area in various types of forest cover as well as in urban or agricultural situations. The amount of added fructification through the use of the fungus as a biological control agent was determined from inoculated plots as well as from calculated stump-surface areas developed from published stand-density data. Added fructification was multiplied by a factor representing the maximum biological control frequency in order to compare added fructification with natural fructification values. From the various calculations, it was determined that the added fructification ofC. purpureumis of the same order of magnitude as naturally occurring levels or even lower. In addition, there is a distinct geographical separation between predominantly forestry and predominantly settled areas where fruit and ornamental trees are cultivated. Accordingly, it was concluded that using the fungus as a biological control agent in forestry is not likely to pose a significant threat to fruit growing and commercial forests.     

Human Interindividual Variability in Cancer Risks—Technical and Management Challenges

Existing risk assessment procedures for carcinogens are intended to be “conservative” in the uncertainty dimension—giving estimates that are expected to be higher than true risks for typical people. However, these procedures do not consider the likely variability in susceptibility among individual people. This paper updates previous estimates of the likely extent of this variability for metabolically activated, genetically-acting carcinogens based on recent information on human interindividual variability in metabolic activation, detoxification, and DNA repair. The resulting expected skewness of cancer risk distributions is estimated using Monte Carlo simulations of both variability and uncertainty.

Some risk management implications are:

1. When evaluating the fairness of a particular risk distribution, managers need to gain familiarity with a three-dimensional characterization—X level of risk, for the Yth percentile individual (addressing variability) with Z degree of confidence (addressing uncertainty).

2. To the extent that variability distributions are skewed (e.g., with a long tail extending to high values) population mean risks will tend to exceed risks for median individuals. Together with the skewness in uncertainty distributions, this implies that “expected value” estimates of aggregate population risks—the estimates of interest for cost benefit analyses—are likely to be closer to traditional upper confidence limit risk estimates than has often been assumed in the past.

Defining risk: Normative considerations

The public thinks about (i.e., defines) environmental human health risks in different terms than the “experts.”; And because the manner in which we conceive of risk goes a long way in determining how risk management is conceived and carried out, any definition of risk has important normative elements. I argue that environmental policy based on the public's conception of risk fails to adequately protect fundamental human rights to health and liberty, by taking undue account of certain psychological factors that enter into the public's perception of risk. A survey of some of these factors is offered in an attempt to determine their policy relevance. The traditional scientific conception of risk, although not adequate to entirely define risk policy, serves as an important anchor for the protection of these rights by focusing on the probability or number of adverse health effects.     

Noncancer Risk Assessment: A Probabilistic Alternative to Current Practice

Based on imperfect data and theory, agencies such as the United States Environmental Protection Agency (USEPA) currently derive “reference doses” (RfDs) to guide risk managers charged with ensuring that human exposures to chemicals are below population thresholds. The RfD for a chemical is typically reported as a single number, even though it is widely acknowledged that there are significant uncertainties inherent in the derivation of this number.

In this article, the authors propose a probabilistic alternative to the EPA's method that expresses the human population threshold as a probability distribution of values (rather than a single RfD value), taking into account the major sources of scientific uncertainty in such estimates. The approach is illustrated using much of the same data that USEPA uses to justify their current RfD procedure.

Like the EPA's approach, our approach recognizes the four key extrapolations that are necessary to define the human population threshold based on animal data: animal to human, human heterogeneity, LOAEL to NOAEL, and subchronic to chronic. Rather than using available data to define point estimates of “uncertainty factors” for these extrapolations, the proposed approach uses available data to define a probability distribution of adjustment factors. These initial characterizations of uncertainty can then be refined when more robust or specific data become available for a particular chemical or class of chemicals.

Quantitative characterization of uncertainty in noncancer risk assessment will be useful to risk managers who face complex trade-offs between control costs and protection of public health. The new approach can help decision-makers understand how much extra control cost must be expended to achieve a specified increase in confidence that the human population threshold is not being exceeded.     

Prosimian juvenile mortality in zoos and primate centers

I review literature on juvenile mortality of captive prosimians in order to evaluate the available information on captive breeding. Juvenile mortality includes abortion, premature mortality, stillbirth, and death of the unweaned young. Prosimian juvenile mortality ranges between 25 and 45% in captive populations. It is generally lower in the Lemuroidea, particularly the Cheirogaleidae, than in the Lorisoidea. Mortality is particularly high in the Lorisinae. Most mortality, including a high stillbirth rate, occurs on the first day and during the first 10 days thereafter. Stress, maternal neglect and traumatic insults, not infrequently linked to each other, are the most frequently reported causes of death. The percentage of congenital malformations tends to be high in some colonies. Sex of the infant and parity seem to be important risk factors for juvenile mortality, whereas litter size does not appear to be important. Based on few data, wild- caught females appear to have higher breeding success than those born in captivity. Synchronized births in lemuroids and isolated births in Galagoare more likely to result in successfully weaned infants.     

Physical Activity,Obesity, and Cardiovascular Risk Factors in Children. The Belgian Luxembourg Child Study II

GUILLAUME, MICHÈLE, LEIF LAPIDUS, PER BJÖRNTORP, ANDRE LAMBERT. Physical activity, obesity, and cardiovascular risk factors in children. The Belgian Luxembourg Child Study II. Physical activity was measured in relation to cardiovascular (CV) risk factors in a randomly selected population of 1028 children from Province de Luxembourg in Belgium, a mainly rural area with a high prevalence of such risk factors among adults and children. Physical activity was estimated as participation in sport activities, a major indicator of leisure-time physical activity in schoolchildren, and physical inactivity was estimated as frequency and duration of television (TV) watching. Boys participated more frequently in sport activities than girls did (p=0. 001). A majority of the children watched TV daily. After age adjustment, bodyweight (girls, p<0. 012; boys, p<0. 027) and, in boys, body mass index (BMI) (p<0. 039) were related to days per week of TV watching. No significant relationships with other CV risk factors remained after adjustments for BMI. In analyses of independent contributions of age, TV watching, and sports activity on CV risk factors, age showed highly significant relationships. In boys, TV showed relationships with BMI (P<0. 04) and (borderline) with systolic blood pressure, independent of age and sports activity, whereas the latter was significantly related to subscapular skinfold (p<0. 04) and (borderline) with triceps skinfold and cholesterol. In girls, no significant independent contributions to risk factor associations were found. The father's education was directly associated with sports activities, whereas the mother being a housewife showed negative relationships to physical activity and positive to TV watching in their children, suggesting socioeconomic influence on the activity patterns of children. Furthermore, registrations suggested less physical activity in the most rural part of the area. It is concluded that children in this mainly rural area watch TV frequently. In boys, physical inactivity, measured both as TV watching and as registrations of sports activities, contributes independently to body fat mass. In girls, no contribution or weaker contributions of physical inactivity were found. This suggests that contributory factors leading to obesity might be different in girls and boys.