Chromosome distribution studies after inorganic lead exposure

Summary We studied the chromosome distribution in persons professionally exposed to inorganic lead. The degree of lead exposure was evaluated by biochemical measurements and cytogenetic analysis. The chromosome distribution was analyzed from trypsin banded karyotypes; in particular we studied centromere distances ² and centromere-metaphase-center distances (d²) which were obtained by computer-aided mathematical transformation of the individual metaphase coordinates.Higher concentrations of blood lead and urine -ALA and a statistically significant increase in aneuploidy, hypoploidy, and type-B chromosome aberrations revealed appreciable exposure although none of the subjects showed signs of excessive lead absorption.However study of the chromosome distribution showed no major differences with that of the controls indicating that lead acts preferentially (directly or indirectly) on the chromosomes rather than on the spindle apparatus. A dissociation of the acrocentric chromosomes was observed in the lead group when compared with the controls. This is thought to reflect a secondary action of lead on the nucleolar organiser regions.     

Chromosome changes with time in lymphocytes after occupational exposure to toluene

Chromosome analyses were carried out in peripheral lymphocytes of 27 workers exposed to toluene in a rotogravure plant. At the time of blood sampling all of them had not been exposed to toluene for at least 4 months up to 5 years. Up to 2 years after cessation of exposure to toluene a higher incidence of chromatid-type aberrations could be observed than in controls. After longer post-exposure periods the aberration yields can no longer be distinguished from background level. No differences were revealed in SCE frequencies of smoking or non-smoking workers post toluene exposure compared with the corresponding controls.     

Chromosome aberrations in lymphocytes of mice after sub-acute low-level inhalation exposure to benzene

Male and female CD-1 mice were exposed to near ambient air concentrations of benzene by inhalation for 22 h per day, 7 days per week for 6 weeks. The concentrations were 0, 40, 100 and 1000 ppb. Significant increases in chromosome aberrations in spleen lymphocytes were observed in exposed compared with control mice except in the high-dose group (p less than 0.05 for female mice in 2 experiments and for male mice in 1 experiment; p less than 0.15 for male mice in the second experiment). A lack of increase in aberrations among mice of the high-dose group may be due to an induction of detoxifying enzymes as observed by us in a previous study (Au et al., 1988b). We also found that the female mice were more sensitive to the clastogenic activity of benzene than male mice under our experimental conditions. Our study serves to emphasize the need to conduct subchronic, low-dose in vivo genotoxicity studies using exposure conditions similar to those of humans, for evaluation of potential hazards. Our data suggest that the current occupational exposure concentrations for benzene (less than 1000 ppb) may still be hazardous to humans.     

Surface soil as a potential source of lead exposure for young children.

Soil analyses revealed an elevated lead content in the surface soil of three British Columbia cities. The lead accumulations were largely attributed to dustfall from a nearby large lead-zinc smelter in Trail and to automotive traffic in Nelson and Vancouver. Although the mean concentrations of lead in the soil were relatively low at Nelson (192 parts per million [ppm]), in selected areas of Vancouver with heavy traffic they were similar to those found within 1.6 km of the large smelter at Trail (1545 and 1662 ppm respectively). In a study conducted in 1975, children aged 1 to 6 years in Trail and Nelson were found to have higher mean blood lead levels than grade nine students. The findings of the later study support the view that particulate lead in surface soil and dust accounted for most of the greater lead absorption in the younger children.     

Rat renal carcinogenesis after chronic simultaneous exposure to lead acetate and N-nitrosodiethylamine

Chronic oral administration of lead acetate and/or N-nitrosodiethylamine to rats produces three different types of renal cell tumors composed of basophilic, chromophobic or oncocytic cells. The most frequent tumor, often visible macroscopically, is made up of basophilic cells and forms tubular, cystic, pseudo-papillary or solid structures; it may show considerable cellular atypia but does not metastasize or invade the surrounding parenchyma. Chromophobic and oncocytic tumors are rare and can only be detected with the microscope; they usually form cystic or solid structures. Basophilic and chromophobic tumors arise from specific segments of the proximal tubules, characteristic for each carcinogen: P2, P3C and P3M for lead acetate; P2 and P3C for N-nitrosodiethylamine. Karyomegalia in proximal tubule cells appears to be irrelevant in renal carcinogenesis. However, the appearance of basophilic and chromophobic cells in P2, P3C and P3M segments is considered to be an early change in tumor development. Oncocytic microadenomas originate from collecting ducts showing focal oncocytic transformation. Synergistic or inhibitory effects are not observed after chronic simultaneous administration of lead acetate and N-nitrosodiethylamine, although both carcinogens act in common on P2 and P3C proximal tubule segments.     

Chromosome aberration frequencies and chromosome instability in mice after long-term exposure to low-dose-rate gamma-irradiation

Chronological changes of chromosome aberration rates related to accumulated doses in chronically exposed humans and animals at a low-dose-rate have not been well studied. C3H female specific pathogen-free mice (8 weeks of age) were chronically irradiated. Chromosome aberration rate in mouse splenocytes after long-term exposure to low-dose-rate (LDR) gamma-rays was serially determined by conventional Giemsa method. Incidence of dicentrics and centric rings increased almost linearly up to 8000 mGy following irradiation for about 400 days at a LDR of 20 mGy/day. Clear dose-rate effects were observed in the chromosome aberration frequencies between dose rates of 20 mGy/day and 200 Gy/day. Furthermore, the frequencies of complex aberrations increased as accumulated doses increased in LDR irradiation. This trend was also observed for the incidences of micronuclei and trisomies of chromosomes 5, 13 and 18 in splenocytes, detected by micronucleus assay and metaphase fluorescence in situ hybridization (FISH) method, respectively. Incidences of 2-4 micronuclei and trisomy increased in mouse splenocytes after irradiation of 8000 mGy at a LDR of 20 mGy/day. These complex chromosome aberrations and numerical chromosome aberrations seem to be induced indirectly after radiation exposure and thus the results indicate that continuous gamma-ray irradiation for 400 days at LDR of 20 mGy/day induced chromosomal instability in mice. These results are important to evaluate the biological effects of long-term exposure to LDR radiation in humans.     

Assessment of ecological risks in weed biocontrol: Input from retrospective ecological analyses

Prediction of the outcomes of natural enemy introductions remains the most fundamental challenge in biological control. Quantitative retrospective analyses of ongoing biocontrol projects provide a systematic strategy to evaluate and further develop ecological risk assessment. In this review, we highlight a crucial assumption underlying a continued reliance on the host specificity paradigm as a quantitative prediction of ecological risk, summarize the status of our retrospective analyses of nontarget effects of two weevils used against exotic thistles in North America, and discuss our prospective assessment of risk to a federally listed, threatened species (Cirsium pitcheri) based on those studies. Our analyses quantify the fact that host range and preference from host specificity tests are not sufficient to predict ecological impact if the introduced natural enemy is not strictly monophagous. The implicit assumption when such use is made of the host specificity data in risk assessment is that population impacts are proportional to relative preference and performance, the key components of host specificity. However, in concert with shifting awareness in the field, our studies demonstrate that the environment influences and can alter host use and population growth, leading to higher than expected direct impacts on the less preferred native host species at several spatial scales. Further, we have found that straightforward, easily anticipated indirect effects, on intraguild foragers as well as on the less preferred native host plant species, can be both widespread and significant. We conclude that intensive retrospective ecological studies provide some guidance for the quantitative prospective studies needed to assess candidate biological control agent dynamics and impacts and, so, contribute to improved rigor in the evaluation of total ecological risk to native species.     

Chromosome identification and comparative karyotypic analyses of four Pinus species

Chromosomal landmarks in four Pinus species: P. densiflora, P. thunbergii, P. sylvestris, and P. nigra were identified by fluorescence in situ hybridization (FISH) using hapten- or fluorochrome-labeled probes for the plant telomere repeat, centromeric repeat (PCSR), and rDNA. FISH landmarks were located at the interstitial and proximal regions of chromosomes and allowed us to identify nearly all of the homologous chromosomes in each species. A comparative analysis of the FISH karyotypes among the four species showed that the interstitial FISH signals obtained by hybridization with the telomere and rDNA sequences were stable and could be used to identify homologous chromosomes among species. The identification of homologous chromosomes among species facilitated a detailed comparative karyotype analysis. The results suggest that the degree of chromosomal differentiation among the four Pinus species is very low and that the proximal regions vary in their DNA sequences. The similarities and differences among FISH karyotypes are discussed in relation to phylogeny.