DNA damage and repair in cells of lead exposed people

The Comet Assay as a Tool in Human Biomonitoring Studies of Environmental and Occupational Exposure to Chemicals-A Systematic Scoping Review

Biomonitoring of human populations exposed to chemical substances that can act as potential mutagens or carcinogens, may enable the detection of damage and early disease prevention. In recent years, the comet assay has become an important tool for assessing DNA damage, both in environmental and occupational exposure contexts. To evidence the role of the comet assay in human biomonitoring, we have analysed original research studies of environmental or occupational exposure that used the comet assay in their assessments, following the PRISMA-ScR method (preferred reporting items for systematic reviews and meta-analyses extension for scoping reviews). Groups of chemicals were designated according to a broad classification, and the results obtained from over 300 original studies (n = 123 on air pollutants, n = 14 on anaesthetics, n = 18 on antineoplastic drugs, n = 57 on heavy metals, n = 59 on pesticides, and n = 49 on solvents) showed overall higher values of DNA strand breaks in the exposed subjects in comparison with the unexposed. In summary, our systematic scoping review strengthens the relevance of the use of the comet assay in assessing DNA damage in human biomonitoring studies.

Assessment of heavy metals among auto workers in metropolitan city: a case study

In recent decades, heavy metals (HMs) have emerged as a global health concern. Unfortunately, in Pakistan, there is a general lack of awareness regarding the potential health risks associated with HMs pollution among automobile workers. Herein, we investigated the concentration of heavy metals such as lead (Pb), cadmium (Cd), and chromium (Cr) among automobile workers who were occupationally exposed in Mingora City, Khyber Pakhtunkhwa, Pakistan. Three different automobile groups, i.e., battery recyclers, spray painters, and mechanics were studied in detail. A total of 40 blood samples were collected from automobile workers groups while 10 blood samples were collected as control individuals from different locations in the study area. We investigated heavy metals concentration with a standard method using an atomic absorption spectrometer AAS (PerkinElmer Analyst 700, United States). Based on our findings, the battery recycling group displayed the most elevated Pb levels (5.45 ± 2.11 μg/dL), exceeding those of both the spray painters' group (5.12 ± 1.98 μg/dL) and the mechanics' group (3.79 ± 2.21 μg/dL). This can be attributed to their higher exposure to Pb pollution resulting from the deterioration, dismantling, grinding, or crushing of old batteries. In the context of chromium (Cr) exposure, a similar trend was observed among the battery recycling group, as well as the spray painters and mechanics groups. However, in the case of cadmium (Cd), the mechanics' group exhibited the highest level of exposure (4.45 ± 0.65 μg/dL), surpassing the battery recycling group (1.17 ± 0.45 μg/dL) and the spray painters' group (1.35 ± 0.69 μg/dL), which was attributed to their greater exposure to welding fumes and other activities in their workplace. We believe that our findings will encourage regulatory measures to improve the health of automobile workers. However, further work is needed to determine various health-related issues associated with heavy metal exposure among automobile workers.

Serum metallomics reveals insights into the associations of elements with the progression of preleukemic diseases toward acute leukemia

Acute leukemia (AL) is a critical neoplasm of white blood cells with two main subtypes: acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). This study is focused on understanding the association of the preleukemic disease aplastic anemia (APA) with ALL and AML at metallomic level, using healthy subjects as a control. In this study, a validated and efficient inductively coupled plasma-mass spectrometry/MS-based workflow was employed to profile a total of 13 metallomic features. The study encompassed 41 patients with AML, 62 patients with ALL, 46 patients with APA, and 55 age-matched healthy controls. The metallomic features consisted of eight essential elements (Ca, Co, Cu, Fe, Mg, Mn, Se, and Zn) and five non-essential/toxic elements (Ag, Cd, Cr, Ni, and Pb). Six out of the 13 elements were found to be substantially different (P < .05) using absolute concentrations between serum samples of AL (ALL and AML) and preleukemia (APA) patients in comparison with healthy subjects. Elements including magnesium, calcium, iron, copper, and zinc were upregulated and only one element (chromium) was downregulated in serum samples of disease when compared with healthy subjects. Through the utilization of both univariate tests and multivariate classification modeling, it was determined that chromium exhibited a progressive behavior among the studied elements. Specifically, chromium displayed a sequential upregulation from healthy individuals to preleukemic disease (APA), and ultimately in patients diagnosed with ALL. Overall, metallomic-based biomarkers may have the utility to predict the association of APA with ALL.

Impact of Heavy Metals on Glioma Tumorigenesis

Recently, an increase in the incidence of brain tumors has been observed in the most industrialized countries. This event triggered considerable interest in the study of heavy metals and their presence in the environment (air, water, soil, and food). It is probable that their accumulation in the body could lead to a high risk of the onset of numerous pathologies, including brain tumors, in humans. Heavy metals are capable of generating reactive oxygen, which plays a key role in various pathological mechanisms. Alteration of the homeostasis of heavy metals could cause the overproduction of reactive oxygen species and induce DNA damage, lipid peroxidation, and the alteration of proteins. A large number of studies have shown that iron, cadmium, lead, nickel, chromium, and mercury levels were significantly elevated in patients affected by gliomas. In this study, we try to highlight a possible correlation between the most frequently encountered heavy metals, their presence in the environment, their sources, and glioma tumorigenesis. We also report on the review of the relevant literature.

Prognostic biomarker prediction for glioma induced by heavy metals and their mixtures: An in-silico study

Although there is an association between heavy metals and glioma, the molecular mechanisms involved in glioma development remain unclear. Therefore, this study aimed to assess the molecular mechanisms implicated in glioma development induced by heavy metals and their mixtures using various methodologies and databases (CTD, Google Scholar, PubMed, ScienceDirect, SpringerLink, miRNAsong, GeneMANIA, Metascape, MIENTURNET, UALCAN). I found that heavy metals, particularly arsenic, mercury, lead, and cadmium, as well as their mixtures, have substantial influences on the etiology of gliomas. "glioblastoma signaling pathways," "integrated cancer pathway," "central carbon metabolism in cancer," "microRNAs in cancer," "p53 signaling pathway," "chemical carcinogenesis-DNA adducts," "glioma," "TP53 network," and "MAPK signaling pathway" were the predominant molecular pathways implicated in the glioma development induced by the studied heavy metals and their mixtures. Five genes (SOD1, CAT, GSTP1, PTGS2, TNF), two miRNAs (hsa-miR-26b-5p and hsa-miR-143-3p), and transcription factors (DR1 and HNF4) were identified as key components related to combined heavy metal and glioma development. Physical interactions were found to be the most common among the heavy metals and their mixtures studied (ranging from 45.2% to 77.6%). The expression level of SOD1 was significantly lower in glioblastoma multiforma samples compared to normal samples, whereas GSTP1 and TP53 expression levels were significantly higher. Brain lower and grade glioma patients who had higher levels of TP53, hsa-miR-25, hsa-miR-34, hsa-miR-222, and hsa-miR-143 had a reduced likelihood of survival. Our findings suggest that further priority should be given to investigating the impact of specific heavy metals or their mixtures on these molecular processes.

Role of Ape1 in Impaired DNA Repair Capacity in Battery Recycling Plant Workers Exposed to Lead

Exposure to lead in environmental and occupational settings continues to be a serious public health problem. At environmentally relevant doses, two mechanisms may underlie lead exposition-induced genotoxicity, disruption of the redox balance and an interference with DNA repair systems. The aim of the study was to evaluate the ability of lead exposition to induce impaired function of Ape1 and its impact on DNA repair capacity of workers chronically exposed to lead in a battery recycling plant. Our study included 53 participants, 37 lead exposed workers and 16 non-lead exposed workers. Lead intoxication was characterized by high blood lead concentration, high lipid peroxidation and low activity of delta-aminolevulinic acid dehydratase (δ-ALAD). Relevantly, we found a loss of DNA repair capacity related with down-regulation of a set of specific DNA repair genes, showing specifically, for the first time, the role of Ape1 down regulation at transcriptional and protein levels in workers exposed to lead. Additionally, using a functional assay we found an impaired function of Ape1 that correlates with high blood lead concentration and lipid peroxidation. Taken together, these data suggest that occupational exposure to lead could decrease DNA repair capacity, inhibiting the function of Ape1, as well other repair genes through the regulation of the ZF-transcription factor, promoting the genomic instability.

Genotoxic Effects of Lead and Their Impact on the Expression of DNA Repair Genes

Exposure to lead (Pb) continues to be a significant worldwide problem. Pb is a highly poisonous heavy metal affecting several organ systems in the body. Although Pb has been shown to be genotoxic to experimental animals and humans, the underlying mechanisms are still not understood. An indirect mechanism related to the inhibition of DNA repair systems by Pb has been suggested. Heavy metals can interfere with the activities of several proteins and gene expressions. Recent studies gathered in this review article demonstrated an altered expression of DNA repair genes due to Pb toxicity. However, their findings are conflicting. Furthermore, the interaction of Pb and epigenetic mechanisms regulating gene expression may have a crucial role in the inhibition of DNA repair systems. Therefore, additional studies are needed to evaluate these findings and to obtain a complete picture of the genotoxic properties of Pb and the underlying mechanisms that may have a crucial role in carcinogenesis.

Occupational Lead Exposure and Brain Tumors: Systematic Review and Meta-Analysis

(1) Background: Due to inconsistencies in epidemiological findings, there has been uncertainty regarding the association of lead compounds with brain tumors. We performed a meta-analysis of published case-control and cohort studies exploring lead compound exposure and brain tumor risk. (2) Methods: We searched PubMed, Embase^®, and Cochrane to find eligible studies. Eighteen studies were selected for assessment of occupational exposure to lead compound and brain tumor. Pooled estimates of odds ratios (ORs) were obtained using random effects models. We assessed the differences through subgroup analysis according to tumor type, study design, measurements of exposure, and tumor outcome. Statistical tests for publication bias, heterogeneity, and sensitivity analysis were applied. (3) Results: Our systematic review and meta-analysis showed a not significant association with lead exposure and risk of benign and malignant brain tumors (pooled OR = 1.11, 95% Confidence Interval (CI): 0.95–1.29). Including only malignant brain tumors, the risk of brain tumor was significantly increased (pooled OR = 1.13, 95% CI: 1.04–1.24). (4) Conclusions: This meta-analysis provides suggestive evidence for an association between lead compound exposure and brain tumor. In future studies, it will be necessary to identify the effect of lead compounds according to the types of brain tumor.

Subcellular partitioning of cadmium and lead in Eisenia fetida and their effects to sperm count, morphology and apoptosis

Earthworms and their biomarkers are considered good indicators for assessing the effects of toxic chemicals. Therefore, in this study, we exposed Eisenia fetida to lethal and sub-lethal concentrations of Cd and Pb nitrate in artificial soil for 14 and 28 days to evaluate the impact on subcellular partitioning, lethal toxicity (LC₅₀), growth, sperm count, morphology and apoptosis (using TUNEL assay). The soluble internal pools of both metals were good predictors of the responses of biomarkers. We found sperm deformation, TUNEL positive sperms and weight loss positively and sperm count negatively correlated with the concentrations of Cd and Pb in the total internal and cytosolic fraction (p < 0.01) and to a lesser extent with Pb concentrations in the granular fraction (p < 0.05). Fourteen days LC₅₀ for Cd and Pb were 2169 ± 322 and 6387 ± 904 μg/g, respectively. Cadmium and Pb caused a significant depression in sperm count after 14 (Cd: up to 46.9%; Pb: up to 36.24%) and 28 (Cd: up to 72.47%; Pb: up to 43.12%) days of exposure relative to the control (p < 0.05). Cadmium induced higher abnormality in sperm heads than Pb. For both metals, TUNEL positive sperms significantly increased after 14 (Cd: up to 14.17%; Pb: up to 16.33%) and 28 (Cd: up to 16.33%; Pb: up to 11.67%) days of exposure compared with the control (p < 0.05). The findings of this study, illustrate the importance of considering sperm parameters as a rapid, easy and sensitive biomarker for the evaluation of metal toxicity.

Carcinogenic and non-carcinogenic risk assessment of heavy metals contamination in duck eggs and meat as a warning scenario in Thailand

The aim of this study was to determine the levels of Pb, Cd, Co and Cr in duck eggs and duck meat and to assess the risk of carcinogenic and non-carcinogenic effects caused by the consumption of duck products collected in Thailand. The human health risk assessment refers to the formulation of the USEPA standard focused on Estimated Daily Intake (EDI), Incremental Lifetime Cancer Risk (ILCR), Target Hazard Quotient (THQ) and Total Target Hazard Quotient (TTHQ). Ninety-eight percent of duck egg samples in this study were contaminated with Pb, with the average level typically above the standard limit. The EDI evaluation of heavy metal in children was the highest for all metals in the eggs. The calculated ILCR levels of Pb, Cd and Cr in eggs and meat consumption were higher than 10^-4 in children, adults, males, and females. Children were at risk when consuming contaminated duck eggs and the risk was higher than in adults by 3.9 times for Pb, Cd and Cr. This finding suggests that there is a high probability of cancer risk, particularly for children, which is higher than adults by absorption of these carcinogenic heavy metals through eggs. The calculation of THQ if consuming heavy metals contaminated duck eggs and meat in human exposure (70years) could conclude that the THQ male was higher than the female for all metals. However, the calculations of TTHQ for Pb, Cd, Co and Cr contamination in a duck egg and meat scenario for adults, males and females were still below the standard limit of 1, which means there was no risk, although there could be adverse health effects. This study suggested that children should be the focus of long-term monitoring for evaluating the carcinogenicity of these metals, more specifically in males.

Assessment of lead exposure among automobile technicians in Khyber Pakhtunkhwa, Pakistan

Exposure to Pb among automobile technicians in selected towns of Khyber Pakhtunkhwa Province, Pakistan, was studied using a questionnaire, biological sampling (blood, hair, nails), and analysis of Pb biomonitoring data across various subgroups of occupation, age, and years of exposure. The study population included exposed automobile technicians (n=50) and a control group (n=50). The automobile technicians were further stratified into 4 groups: mechanics, auto-body technicians, electricians, and painters. Mean Pb levels in biological samples of the automobile technicians were significantly higher than in the control group (P<0.01). The Pb concentrations (mean±standard deviation) in whole blood, hair, and nails of automobile technicians were 65.3±41.9μgdL^-1, 23.6±11.2mgkg^-1 and 29.7±14.5mgkg^-1, respectively, whereas concentrations in the control group were 21.7±17.6μgdL^-1, 4.8±3.4mgkg^-1 and 7.2±3.9mgkg^-1. Fifty two percent of the automobile technicians had blood levels >50μgdL^-1, but only 14% of the control group exceeded this level. Considering that Pb blood levels of 50μgdL^-1 exceed maximum concentrations recommended by leading public health organizations, appropriate measures should be taken to protect the welfare of the exposed automobile technicians and their families.

Genotoxicity of 11 heavy metals detected as food contaminants in two human cell lines

Heavy metals, such as arsenic (As), antimony (Sb), barium (Ba), cadmium (Cd), cobalt (Co), germanium (Ge), lead (Pb), nickel (Ni), tellurium (Te), and vanadium (V) are widely distributed in the environment and in the food chain. Human exposure to heavy metals through water and food has been reported by different international agencies. Although some of these heavy metals are essential elements for human growth and development, they may also be toxic at low concentrations due to indirect mechanisms. In this study, the genotoxic and cytotoxic properties of 15 different oxidation statuses of 11 different heavy metals were investigated using high-throughput screening (γH2AX assay) in two human cell lines (HepG2 and LS-174T) representative of target organs (liver and colon) for food contaminants. Base on their lowest observed adverse effect concentration, the genotoxic potency of each heavy metal in each cell line was ranked in decreasing order, NaAsO₂  > CdCl₂  > PbCl₂ (only in LS-174T cells) > As₂ O₅  > SbCl₃  > K₂ TeO₃  > As₂ O₃ . No significant genotoxicity was observed with the other heavy metals tested. Cell viability data indicate that several heavy metals (As, Cd, Co, Ni, Sb, and Te) induce cytotoxicity at high concentrations, whereas an increase in the number of cells was observed for lead concentrations >100 µM in both cell lines tested, suggesting that lead stimulates cell growth. All these results highlight the possible human health hazards associated with the presence of heavy metals present in food. Environ. Mol. Mutagen. 59:202-210, 2018. © 2017 Wiley Periodicals, Inc.

Evaluation of DNA damage and DNA repair capacity in occupationally lead-exposed workers

Occupational lead (Pb) exposure remains a significant concern for workers in Turkey. Health hazards of Pb exposure have been investigated in various test systems, but results regarding its potential genotoxic effects on exposed populations are contradictory. In this study, a control group and an exposed group were studied, each consisting of 25 male subjects. Blood lead levels (BLLs) were estimated by graphite furnace atomic absorption spectrometry. Genotoxic effects of Pb exposure were studied in leukocytes by comet and challenge assays. The effect of Pb exposure to DNA repair capacity was evaluated following in vitro hydrogen peroxide exposure. Pb-exposed workers had significantly higher BLLs than the control group ( p < 0.01). DNA damage in exposed workers had a significantly higher percentage of DNA in tail than the control group ( p < 0.05). In the challenge assay, it was found that the mean DNA% repair capacity was significantly decreased in Pb-exposed workers ( p < 0.01). The results indicated that occupational Pb exposure is associated with DNA damage and causes decrease in DNA% repair capacity, indicating a potential health concern for occupationally Pb-exposed populations.

Results of micronucleus assays with individuals who are occupationally and environmentally exposed to mercury, lead and cadmium

Millions of humans are exposed occupationally and environmentally to lead, mercury and cadmium compounds. Mercury compounds are less abundant but some of them belong to the most toxic chemicals which are known. We evaluated the literature to find out if these metals act in humans as genotoxic carcinogens and if their health effects can be predicted by use of micronucleus (MN) assays with lymphocytes and/or with other genotoxicity tests. Numerous studies showed that lead and mercury induce cancer in humans and also in animals, in vitro experiments with cultured cells indicate that they cause DNA damage via different molecular mechanisms including release of reactive oxygen species and interactions with DNA repair processes. Also in most human studies, positive results were obtained in MN tests with lymphocytes (all 15 occupational studies with lead yielded positive results, with mercury 6 out of 7 investigations were positive). For cadmium, there is clear evidence that it causes cancer in humans; however, induction of chromosomal damage was only seen in high dose experiments with mammalian cells while results of animal and human studies yielded conflicting results (only in 2 of 5MN trials with humans positive findings were reported). Possibly, non-genotoxic mechanisms such as inhibition of apoptosis and interaction with signaling pathways account for the carcinogenic properties of cadmium species. The findings of MN studies with lead and mercury are in excellent agreement with results which were obtained with other endpoints (e.g. chromosomal aberrations and comet formations) and it is evident that this approach can be used for occupational and environmental monitoring of exposed individuals. Important future tasks will be the realization of larger studies with a uniform standardized protocol, the additional evaluation of anomalies other than MN (nuclear buds and bridges) and the combination of such trials with investigations which allow to define the molecular mechanisms relevant for exposed humans.

Occupational Lead Exposure and Associations with Selected Cancers: The Shanghai Men's and Women's Health Study Cohorts

BACKGROUND

Epidemiologic studies of occupational lead exposure have suggested increased risks of cancers of the stomach, lung, kidney, brain, and meninges; however, the totality of the evidence is inconsistent.

OBJECTIVE

We investigated the relationship between occupational lead exposure and cancer incidence at the five abovementioned sites in two prospective cohorts in Shanghai, China.

METHODS

Annual job/industry-specific estimates of lead fume and lead dust exposure, derived from a statistical model combining expert lead intensity ratings with inspection measurements, were applied to the lifetime work histories of participants from the Shanghai Women's Health Study (SWHS; n = 73,363) and the Shanghai Men's Health Study (SMHS; n = 61,379) to estimate cumulative exposure to lead fume and lead dust. These metrics were then combined into an overall occupational lead exposure variable. Cohort-specific relative hazard rate ratios (RRs) and 95% confidence intervals (CIs) comparing exposed and unexposed participants were estimated using Cox proportional hazards regression and combined by meta-analysis.

RESULTS

The proportions of SWHS and SMHS participants with estimated occupational lead exposure were 8.9% and 6.9%, respectively. Lead exposure was positively associated with meningioma risk in women only (n = 38 unexposed and 9 exposed cases; RR = 2.4; 95% CI: 1.1, 5.0), particularly with above-median cumulative exposure (RR = 3.1; 95% CI: 1.3, 7.4). However, all 12 meningioma cases among men were classified as unexposed to lead. We also observed non-significant associations with lead exposure for cancers of the kidney (n = 157 unexposed and 17 ever exposed cases; RR = 1.4; 95% CI: 0.9, 2.3) and brain (n = 67 unexposed and 10 ever exposed cases; RR = 1.8; 95% CI: 0.7, 4.8) overall.

CONCLUSIONS

Our findings, though limited by small numbers of cases, suggest that lead is associated with the risk of several cancers in women and men.

CITATION

Liao LM, Friesen MC, Xiang YB, Cai H, Koh DH, Ji BT, Yang G, Li HL, Locke SJ, Rothman N, Zheng W, Gao YT, Shu XO, Purdue MP. 2016. Occupational lead exposure and associations with selected cancers: the Shanghai Men's and Women's Health Study cohorts. Environ Health Perspect 124:97-103; http://dx.doi.org/10.1289/ehp.1408171.

Heavy metals and epigenetic alterations in brain tumors

Heavy metals and their derivatives can cause various diseases. Numerous studies have evaluated the possible link between exposure to heavy metals and various cancers. Recent data show a correlation between heavy metals and aberration of genetic and epigenetic patterns. From a literature search we noticed few experimental and epidemiological studies that evaluate a possible correlation between heavy metals and brain tumors. Gliomas arise due to genetic and epigenetic alterations of glial cells. Changes in gene expression result in the alteration of the cellular division process. Epigenetic alterations in brain tumors include the hypermethylation of CpG group, hypomethylation of specific genes, aberrant activation of genes, and changes in the position of various histones. Heavy metals are capable of generating reactive oxygen assumes that key functions in various pathological mechanisms. Alteration of homeostasis of metals could cause the overproduction of reactive oxygen species and induce DNA damage, lipid peroxidation, and alteration of proteins. In this study we summarize the possible correlation between heavy metals, epigenetic alterations and brain tumors. We report, moreover, the review of relevant literature.

Amino siloxane oligomer-linked graphene oxide as an efficient adsorbent for removal of Pb(II) from wastewater

A high performance sorbent, oligomer-linked graphene oxide (GO) composite, was prepared through simple cross-linking reactions between GO sheets and poly3-aminopropyltriethoxysilane (PAS) oligomers as crosslinking agents. The three-dimensional PAS oligomers prevented GO sheets from aggregation, provided foreign molecules with easier access, and introduced a large amount of amino functional groups. The morphology, structure and property of the PAS-GO composite were determined by scanning electron microscope (SEM), transmission electron microscope (TEM), Fourie transform infrared (FTIR), X-ray diffractometer (XRD), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The adsorption performance of PAS-GO was investigated in removing Pb(II) ions from water. Compared to 3-aminopropyltriethoxysilane functionalized GO (AS-GO) which was prepared by the direct reaction between 3-aminopropyltriethoxysilane and GO, PAS-GO exhibited much higher adsorptivity toward Pb(II) with the maximum adsorption capacity of 312.5mg/g at 303 K and furthermore the maximum adsorption capacity increased with increasing temperature. The adsorption could be conducted in a wide pH range of 4.0-7.0. Importantly, PAS-GO had a priority tendency to adsorb Pb, Cu and Fe from a mixed solution of metal ions, especially from a practical industrial effluent.

Review: Lead exposure in battery manufacturing and recycling in developing countries and among children in nearby communities

The battery industry is the largest consumer of lead, using an estimated 80% of the global lead production. The industry is also rapidly expanding in emerging market countries. A review of published literature on exposures from lead-acid battery manufacturing and recycling plants in developing countries was conducted. The review included studies from 37 countries published from 1993 to 2010 and excluded facilities in developed countries, such as the United States and those in Western Europe, except for providing comparisons to reported findings. The average worker blood lead level (BLL) in developing countries was 47 μg/dL in battery manufacturing plants and 64 μg/dL in recycling facilities. Airborne lead concentrations reported in battery plants in developing countries averaged 367 μg/m3, which is 7-fold greater than the U.S. Occupational Safety and Health Administration's 50 μg/m3 permissible exposure limit. The geometric mean BLL of children residing near battery plants in developing countries was 19 μg/dL, which is about 13-fold greater than the levels observed among children in the United States. The blood lead and airborne lead exposure concentrations for battery workers were substantially higher in developing countries than in the United States. This disparity may worsen due to rapid growth in lead-acid battery manufacturing and recycling operations worldwide. Given the lack of regulatory and enforcement capacity in most developing countries, third-party certification programs may be the only viable option to improve conditions.

Genotoxic effects of lead: an updated review

Lead is a ubiquitous toxic heavy metal with unique physical and chemical properties that make it suitable for a great variety of applications. Because of its high persistence in the environment and its use since ancient times for many industrial activities, lead is a common environmental and occupational contaminant widely distributed around the world. Even though the toxic effects of lead and its compounds have been investigated for many years in a variety of systems, the data existing with regard to its mutagenic, clastogenic and carcinogenic properties are still contradictory. The International Agency for Research on Cancer has classified lead as possible human carcinogen (group 2B) and its inorganic compounds as probable human carcinogens (group 2A). Furthermore, although the biochemical and molecular mechanisms of action of lead remain still unclear, there are some studies that point out indirect mechanisms of genotoxicity such as inhibition of DNA repair or production of free radicals. This article reviews the works listed in the literature that use different parameters to evaluate the genotoxic effects of lead in vitro, in vivo and in epidemiological studies.

Differences inHPRTmutant frequency among middle-aged Flemish women in association with area of residence and blood lead levels

Biomarkers were measured in residents of Wilrijk and Hoboken, industrial suburbs of the city of Antwerp, and of Peer, a rural municipality in Flanders, Belgium. Persons with known occupational exposures to toxic compounds or commuting over long distances were excluded. Here, we report the hypoxanthine phosphoribosyltransferase gene (HPRT) variant frequencies for 99 non-smoking women aged 50-65 years. HPRT values above the detection limit (V(fpos) values) were observed for 43 subjects (21 from Peer, 22 from Antwerp). The median (10th to 90th percentiles) HPRT variant frequency (V(fpos)) in peripheral lymphocytes was 9.59 (3.44-56.99) for Peer and 3.57 (1.57-13.96) for Antwerp. The V(fpos) value was significantly higher in Peer than in Antwerp, both in terms of crude data (p=0.011) and after correction for age, level of education, smoking status, serum level of selenium and body mass index through analysis of covariance (p=0.011). For the total study population, serum lead concentration showed a non-significant positive correlation with lnV(fpos). In addition, subjects with a blood lead concentration above the median tended to have higher V(fpos) values (9.45x10(-6) for 'high' group versus 5.21x10(-6) for 'low' group; p=0.077 after correction for confounding). Subjects with a serum selenium level above the median tended to have lower V(fpos) values (4.99x10(-6) for 'high' group versus 9.83x10(-6) for 'low' group; p=0.051 after correction for confounding). These data are consistent with an indirect genotoxic effect of lead and with an antimutagenic effect of selenium.

Oxidative stress and immunotoxic effects of lead and their amelioration with myrrh (Commiphora molmol) emulsion

The possible role of Commiphora molmol emulsion (CME) in protecting against lead (PbAc)-induced hepatotoxicity, oxidative stress and immunotoxicity in rabbits was assessed. Six groups of animals were used: groups I (control) and II (PbAc) were not supplemented with CME. Groups III (CME50) and IV (CME50+PbAc) were administered with CME in a dose rate of 50mg/kg bwt, while groups V (CME100) and VI (CME100+PbAc) were received 100mg CME/kg bwt daily p.o for successive 14 weeks. Groups II, IV and VI were given 80 mg PbAc/kg bwt/day orally for 6 weeks starting from the 9th week. At the 12th week, animals were subjected to immunization by a single dose of sheep RBCs. The PbAc-group showed 220% increase in hepatic malondialdehyde levels, while glutathione, glutathione s-transferase and glutathione peroxidase levels decreased. Lead-acetate induced hypoproteinemia and hypoalbuminemia, and increased aminotransferases activity. It reduced the values of lymphocyte transformation test, phagocytic activity, phagocytic index and antibody titer against sheep SRBCs. Interestingly, pretreatment with CME attenuated these adverse effects in a dose-dependent protection. CME, therefore, is a potent antioxidant, and can protect against PbAc-induced hepatic oxidative damage and immunotoxicity by reducing lipid peroxidation and enhancing the antioxidant and immune defense mechanisms.

Induction of excision repairable DNA lesions in lymphocytes exposed to lead and ALA in vitro

Numbers of studies have been carried out on the potential of lead genotoxicity. The mechanisms of lead genotoxicity are not fully known but partly attributed to the formation of highly reactive oxygen metabolites (ROM). However, lead ions have no ability to generate ROM. In this study, we have investigated the ability of lead and ALA to induce excision repairable DNA lesions by using cytosine arabinoside or cytokinesis block micronucleus (ARA-C/CBMN) assay. N-methyl-N-nitrosourea was used as a positive control which is a mutagen and known to induce excision repair. The results of the ARA-C/CBMN assay show that ALA exposures have significantly (p < 0.01) increased the ratio of excision repairable DNA lesions in peripheral blood lymphocytes; however, lead have not. Accordingly, accumulation of ALA should be considered as an effective partner of lead induced DNA damage in lead exposure.

Comparative effects of Cd and Pb on biochemical response and DNA damage in the earthworm Eisenia fetida (Annelida, Oligochaeta)

There are rising concerns about the hazardous effects of cadmium (Cd) and lead (Pb) on the environment in China. Biochemical and comet assays were conducted on the earthworm Eisenia fetida, a suitable bio-indicator organism for evaluating soil pollution after exposure to two heavy metals, Cd and Pb. Protein content increased at low Cd concentrations (p<0.05) and decreased at the highest concentration of 10 mg kg(-1), compared to control (p<0.05). Pb showed an inhibitory effect on protein content at low concentrations but demonstrated no significant effect at higher concentrations. There were no significant differences between control and treated groups at the doses of 1 and 10 mg kg(-1) Cd while at a dose of 0.1 mg kg(-1) Cd the cellulase activity was significantly increased compared to control. Cellulase activities of Pb-treated E. fetida increased in a dose dependent fashion. Results of the comet assay indicated toxicant induced DNA damage. Cd exposure caused significant differences between control and treatment groups (ANOVA, p< 0.05, p< 0.01) and a positive dose-response profile. As for Pb treatment, there were no significant differences between the groups treated with 50 and 500 mg kg(-1) of Pb and the control. Results showed that DNA damage from Cd was more serious than that from Pb. And this indicated that the earthworm was more sensitive to the effects of Cd.

Brain tumor epidemiology: consensus from the Brain Tumor Epidemiology Consortium

Epidemiologists in the Brain Tumor Epidemiology Consortium (BTEC) have prioritized areas for further research. Although many risk factors have been examined over the past several decades, there are few consistent findings, possibly because of small sample sizes in individual studies and differences between studies in patients, tumor types, and methods of classification. Individual studies generally have lacked samples of sufficient size to examine interactions. A major priority based on available evidence and technologies includes expanding research in genetics and molecular epidemiology of brain tumors. BTEC has taken an active role in promoting understudied groups, such as pediatric brain tumors; the etiology of rare glioma subtypes, such as oligodendroglioma; and meningioma, which, although it is not uncommon, has only recently been registered systematically in the United States. There also is a pressing need for more researchers, especially junior investigators, to study brain tumor epidemiology. However, relatively poor funding for brain tumor research has made it difficult to encourage careers in this area. In this report, BTEC epidemiologists reviewed the group's consensus on the current state of scientific findings, and they present a consensus on research priorities to identify which important areas the science should move to address.

Lead, genetic susceptibility, and risk of adult brain tumors

BACKGROUND

Although few etiologic factors for brain tumors have been identified, limited data suggest that lead may increase the risk of brain tumors, particularly meningioma. The ALAD G177C polymorphism affects the toxicokinetics of lead and may confer genetic susceptibility to adverse effects of lead exposure.

METHODS

We examined occupational exposure to lead and risk of brain tumors in a multisite, hospital-based, case-control study of 489 patients with glioma, 197 with meningioma, and 799 non-cancer controls frequency matched on hospital, age, sex, race/ethnicity, and residential proximity to hospital. ALAD genotype was assessed by a Taqman assay for 355 glioma patients, 151 meningioma patients, and 505 controls. Exposure to lead was estimated using a rigorous questionnaire-based exposure assessment strategy incorporating lead measurement and other occupational data abstracted from published articles and reports.

RESULTS

Increased risk of meningioma with occupational lead exposure (estimated by odds ratios and 95% confidence intervals) was most apparent in individuals with the ALAD2 variant allele, for whom risk increased from 1.1 (0.3-4.5) to 5.6 (0.7-45.5) and 12.8 (1.4-120.8) for estimated cumulative lead exposures of 1 to 49 microg/m3-y, 50 to 99 microg/m3-y, and >or=100 microg/m3-y, respectively, compared with unexposed individuals (two-sided P trend = 0.06). This relationship became stronger after excluding occupational lead exposures characterized by a low confidence level or occurring in the 10 years before meningioma diagnosis. Occupational lead exposure was not associated with glioma risk.

CONCLUSIONS

Although our results indicate that lead may be implicated in meningioma risk in genetically susceptible individuals, these results need to be interpreted with caution given the small numbers of exposed cases with a variant genotype.

Environmental lead exposure increases micronuclei in children

The objective of this pilot study was to investigate the contribution of environmental exposures to lead in the development of cytogenetic damage detected as the frequency of micronuclei (MN) in children. The other aim was to apply the MN assay in combination with fluorescence in situ hybridization (FISH) using a pan-centromeric chromosome probe to elucidate the formation mechanism of induced MN. The examined population was composed of 9-year-old children (n = 92), living in the region where non-ferrous ores are extracted and processed. The non-exposed group consisted of 49 children of the same age from an unexposed recreational area. Exposure to lead was assessed by determination of lead concentrations in blood (PbB) by atomic absorption spectrophotometry, whereas the level of selenium (Se) in serum was detected by using graphite furnace atomic-absorption spectrometry. The frequency of MN was determined by the cytokinesis-block MN assay and fluorescence in situ hybridization performed using a specific pan-centromeric probe. Environmental exposure to lead resulted in significantly increased levels of PbB (5.29 +/- 2.09 versus 3.45 +/- 1.20 microg/dl in controls), although the average level was much below the value of the biological exposure limit = 10 microg/dl. A negative correlation between lead in blood and Se in serum concentrations (P = 0.006) was found for the pooled study population. The results showed a significant difference (P < 0.0001) in the level of MN between the exposed and control group (standard MN test: 2.96 +/- 2.36 versus 1.16 +/- 1.28; FISH technique: 3.57 +/- 3.02 versus 1.43 +/- 1.69, respectively). The frequencies of both centromere-positive (C+MN) and centromere-negative (C-MN) micronuclei were significantly increased in exposed children; however, the contribution of C+MN in the total number of MN in peripheral blood lymphocytes of exposed children was significantly higher than in the controls what may suggest a pro-aneugenic effect of the exposure to lead. The results of multiple regression analysis indicated that the exposure to lead was an important factor affecting the increase in MN frequency what was confirmed by significant correlation between the PbB and MN levels. In conclusion, our results suggest that the exposure to lead may be associated with an increased frequency of MN, especially of C+MN; however, the influence of other factors (e.g. vitamins and minerals in the diet) cannot be excluded.

Lead promotes abasic site accumulation and co-mutagenesis in mammalian cells by inhibiting the major abasic endonuclease Ape1

Lead is a widespread environmental toxin, found in contaminated water sources, household paints, and certain occupational settings. Classified as a probable carcinogen by the International Agency for Research on Cancer (IARC), lead promotes mutagenesis when combined with alkylating and oxidizing DNA-damaging agents. We previously reported that lead inhibits the in vitro repair activity of Ape1, the major endonuclease for repairing mutagenic and cytotoxic abasic sites in DNA. We investigated here whether lead targets Ape1 in cultured mammalian cells. We report a concentration-dependent inhibition of apurinic/apyrimidinic (AP) site incision activity of Chinese hamster ovary (CHO) AA8 whole cell extracts by lead. In addition, lead exposure results in a concentration-dependent accumulation of AP sites in the genomic DNA of AA8 cells. An increase in the oxidative base lesion 8-oxoguanine was observed only at high lead levels (500 microM), suggesting that non-specific oxidation plays little role in the production of lead-related AP lesions at physiological metal concentrations--a conclusion corroborated by "thiobarbituric acid reactive substances" assays. Notably, Ape1 overexpression in AA8 (hApe1-3 cell line) abrogated the lead-dependent increase in AP site steady-state levels. Moreover, lead functioned cooperatively to promote a further increase in abasic sites with agents known to generate AP sites in DNA (i.e., methyl methansulfonate (MMS) and hydrogen peroxide (H2O2), but not the DNA crosslinking agent mitomycin C. Hypoxanthine guanine phosphoribosyltransferase (hprt) mutation analysis revealed that, whereas lead alone had no effect on mutation frequencies, mutagenesis increased in MMS treated, and to a greater extent lead/MMS treated, AA8 cells. With the hApe1-3 cell line, the number of mutant colonies in all treatment groups was found to be equal to that of the background level, indicating that Ape1 overexpression reverses MMS- and lead-associated hprt mutagenesis. Our studies in total indicate that Ape1 is a member of an emerging group of DNA surveillance proteins that are inhibited by environmental heavy metals, and suggest an underlying mechanism by which lead promotes co-carcinogenesis.

Evaluating the genotoxic effects of workers exposed to lead using micronucleus assay, comet assay and TCR gene mutation test

To evaluate the genotoxic effects of lead (Pb) exposure, 25 workers in a workplace producing storage battery were monitored for three genetic end-points using micronucleus (MN) assay, comet assay and TCR gene mutation test. Twenty-five controls were matched with workers according to age, gender and smoking. The air Pb concentration in the workplace was 1.26 mg/m(3). All subjects were measured for Pb concentration of blood by atom absorption spectrophotometry. The mean Pb concentration of blood in workers (0.32 mg/l) was significantly higher than that in controls (0.02 mg/l). The results of MN test showed that the mean micronuclei rate (MNR) and mean micronucleated cells rate (MCR) in workers were 9.04+/-1.51 per thousand and 7.76+/-1.23 per thousand, respectively, which were significantly higher than those (2.36+/-0.42 per thousand and 1.92+/-0.31 per thousand) in controls (P<0.01). It was found in the comet assay that the mean tail length (MTL) of 25 workers and 25 controls were 2.42+/-0.09 and 1.02+/-0.08 microm, respectively, there was significant difference between workers and controls for MTL (P<0.01), also the difference of the mean tail moment (MTM) between workers (0.85+/-0.05) and controls (0.30+/-0.09) was very significant (P<0.01). However, in TCR gene mutation assay Mfs-TCR of workers and controls were 1.69+/-0.15 x 10(-4) and 1.74+/-0.17 x 10(-4), respectively, there was no significant difference between workers and controls (P>0.05). The results of our study indicated that the genetic damage was detectable in 25 workers occupationally exposed to lead.

Assessment of abnormal DNA repair responses and genotoxic effects in lead exposed workers

BACKGROUND

One of the main sources of occupational exposure to lead (Pb) in Turkey is in workers of battery industries. Genotoxic studies in human populations exposed to this metal have had conflicting results.

METHODS

Genotoxic effects of Pb were studied in blood cell samples from workers of battery manufactures exposed to Pb compounds by chromosomal aberration (CA) assay and X-ray induced challenge (XRC) assay to assess DNA damage and interference with DNA repair processes after an in vitro exposure of X-ray (1 Gy). The battery manufacturers (n=23) and 23 people who were not occupationally exposed to lead compounds were selected as a control group and classified into categories according to their blood lead levels.

RESULTS

The CA frequencies in the exposed and control group were not significantly different (P>0.05) by conventional CA (CCA) assay, however, the XRC assay demonstrated significantly elevated CAs (P<0.05). Statistically non-significant but reduced DNA repair responses have also been observed in lead exposed workers.

CONCLUSION

The results of this study showed significant increases in the CAs by XRC assay in Pb exposed workers compared to CCA assay. Our data suggests that Pb exposure may cause reduction in DNA repair capacity and these individuals will be more prone to DNA damage. Therefore, preventive measures should be improved against genotoxic risk in workplaces.

Use of primary blood cells for the assessment of exposure to occupational genotoxicants in human biomonitoring studies

The Comet assay is an often used approach for the assessment of genetic damage in primary cells of exposed populations. In the majority of these studies lymphocytes are used. Therefore, we reviewed human biomonitoring studies of occupational exposure using the Comet assay with lymphocytes. We also tried to elucidate the strengths of the studies, which were that (i) data could be obtained in a fast and cost-effective manner, (ii) the ease at which these cells can be collected and (iii) a remarkable concordance between Comet assay and cytogenetic assays. However, the analysis also revealed some shortcomings: (i) the low number of study participants, (ii) the bias in the distribution of gender, (iii) lack of qualitative and quantitative exposure data, (iv) omission to consider differences in physical activity and diet between control and exposed groups, (v) lack of uniformity in the Comet assay procedures, and (vi) controversy in the sensitivity of Comet assay since it picked up DNA damage caused by agents which were found to be weak genotoxicants or non-genotoxicants in other tests, but gave inconsistent results with known mutagens/carcinogens such as cigarette smoke.

The use of the alkaline comet assay with lymphocytes in human biomonitoring studies

We reviewed the data of 45 alkaline comet assay studies with lymphocytes published during the last three years with the objective of monitoring human exposure to genotoxic agents as a result of occupation, drug treatment, diseases or environmental pollution. The strengths of the studies were that: (i) a lot of data could be obtained within a relatively short period of time in a cost-effective manner, (ii) lymphocytes could be easily collected in a non-invasive way and proved to be good surrogate cells in that they picked up effects caused by agents with different cancer target organs and (iii) a remarkable concordance between comet assay and cytogenetic assay data was proved. However, our analysis revealed some shortcomings of the studies such as: (i) the inclusion of low number of study participants and bias in the number and gender of subjects between control and exposed groups, (ii) lack of qualitative and quantitative exposure data, (iii) lack of consideration of differences in physical activity and diet between control and exposed groups, (iv) difficulty in comparison of the studies due to lack of uniformity in the comet assay procedures such as duration of alkali unwinding and electrophoresis, slide scoring method and the metrics used to assess the extent of DNA damage and (v) controversy in the sensitivity of comet assay since it picked up DNA damage caused by agents such as wood dust, pesticides and hormone preparations which were found to be weak genotoxins or non-genotoxins in other tests, but gave inconsistent results with known mutagens/carcinogens such as tobacco smoke. We feel that for the alkaline comet assay to be an important tool in human biomonitoring studies, serious consideration should be given to the flaws in the design and performance of the assay.

Adverse haematological outcome and environmental lead poisoning

The South-eastern Area (SA) of the Municipality of La Spezia (Liguria Region, Italy) is characterised by a heavy environmental lead (Pb) contamination, chiefly due to the emissions of a Pb-processing plant in operation since 1930. In order to assess the risk of Pb poisoning of residents of SA, and to estimate the degree of association between the blood Pb level (BLL) and haematocrit % (HCT), intended as a biomarker of early haematological dysfunction, we reanalysed data of 785 individuals collected in 1992 as a part of a larger national biological monitoring project. Multiple normal regression modelling was applied to estimate the role of residence on log-transformed BLL, and Median Ratio (MR) was used as an index of effect. The same statistical modelling was also applied to reveal the relationship between HCT and BLL. Allowing for several confounders (including occupational exposure to Pb), residents of SA showed a 14% increase (MR=1.14, 95% IC=1.06-1.23%) in the median BLL value compared to people living outside SA. The excess reached 27% (MR=1.27, 95% IC=1.14-1.41%) after 30 years of residence. Parallel results were also obtained in a subgroup composed only of pupils (<18 years, non-smokers, non-drinkers). Finally, regression analysis highlighted a statistically significant parabolic trend in HCT in relation to BLL. The non-linear dose-response relationship, which attests to an adverse effect on the erythrocytic function of BLLs at least over 17.00 microg/dl, is in agreement with the findings of other authors and consistent with the results of an excess occurrence of self-reported anaemia obtained from a previous comparative survey carried out on the same population.

Genotoxic effects of occupational exposure to lead and cadmium

This study was designed to assess genotoxic damage in somatic cells of workers in a Polish battery plant after high-level occupational exposure to lead (Pb) and cadmium (Cd), by use of the following techniques: the micronucleus (MN) assay, combined with in situ fluorescence hybridization (FISH) with pan-centromeric probes, analysis of sister chromatid exchanges (SCEs), and the comet assay. Blood samples from 44 workers exposed to lead, 22 exposed to cadmium, and 52 unexposed persons were used for SCE and MN analysis with 5'-bromodeoxyuridine (BrdU) or cytokinesis block, respectively. In parallel, the comet assay was performed with blood samples from the same persons for detection of DNA damage, including single-strand breaks (SSB) and alkali-labile sites (ALS). In workers exposed mostly to lead, blood Pb concentrations ranged from 282 to 655 microg/l, while the range in the controls was from 17 to 180 microg/l. Cd concentration in lead-exposed workers fell in the same range as for the controls. In workers exposed mainly to cadmium, blood Cd levels varied from 5.4 to 30.8 microg/l, with respective values for controls within the range of 0.2-5.7 microg/l. Pb concentrations were similar as for the controls. The incidence of MN in peripheral lymphocytes from workers exposed to Pb and Cd was over twice as high as in the controls (P<0.01). Using a combination of conventional scoring of MN and FISH with pan-centromeric probes, we assessed that this increase may have been due to clastogenic as well as aneugenic effects. In Cd- and Pb-exposed workers, the frequency of SCEs as well as the incidence of leukocytes with DNA fragmentation in lymphocytes were slightly, but significantly increased ( P<0.05) as compared with controls. After a 3h incubation of the cells to allow for DNA repair, a clear decrease was found in the level of DNA damage in the controls as well as in the exposed workers. No significant influence of smoking on genotoxic damage could be detected in metal-exposed cohorts. Our findings indicate that lead and cadmium induce clastogenic as well as aneugenic effects in peripheral lymphocytes, indicating a potential health risk for working populations with significant exposures to these heavy metals.

In vitro genotoxicity of lead acetate: induction of single and double DNA strand breaks and DNA-protein cross-links

Lead is present in the natural and occupational environment and is reported to interact with DNA, but the mechanism of this interaction is not fully understood. Using the alkaline comet assay we showed that lead acetate at 1-100 microM induced DNA damage in isolated human lymphocytes measured the change in the comet tail length. At 1 and 10 microM we observed an increase in the tail length, whereas at 100 microM a decrease was seen. The former effect could follow from the induction of DNA strand breaks and/or alkali-labile sites (ALS), the latter from the formation of DNA-DNA and/or DNA-protein cross-links. No difference was observed between tail length for the alkaline and pH 12.1 versions of the assay, which indicates that strand breaks and not ALS are responsible for the tail length increase induced by lead. The neutral version of the test revealed that lead acetate induced DNA double-strand breaks at all concentrations tested. The presence of spin traps, 5,5-dimethyl-pyrroline N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN) did not influence the level of DNA damage induced by lead. Post-treatment of the lead-damaged DNA (at 100 microM treatment concentration) by endonuclease III (Endo III) and formamidopyrimidine-DNA glycosylase (Fpg), enzymes recognizing oxidized DNA bases, as well as 3-methyladenine-DNA glycosylase II, an enzyme recognizing alkylated bases, gave rise to a significant increase in the extent of DNA damage. Proteinase K caused an increase in comet tail length, suggesting that lead acetate might cross-link DNA with nuclear proteins. Vitamin A, E, C, calcium chloride and zinc chloride acted synergistically on DNA damage evoked by lead. The results obtained suggest that lead acetate may induce single-strand breaks (SSB) and double-strand breaks (DSB) in DNA as well as DNA-protein cross-links. The participation of free radicals in DNA-damaging potential of lead is not important and it concerns other reactive species than could be trapped by DMPO or PBN.

New measure of DNA repair in the single-cell gel electrophoresis (comet) assay

Since its introduction by Ostling and Johanson [1984; Biochem Biophys Res Commun 123:291-298] and independent modifications by Singh et al. [1990; Exp Cell Res 175:184-191] and Olive et al. [1988; Radiat Res 112:86-94], the comet assay has been widely used in genetic toxicology, environmental biomonitoring, molecular and human epidemiology, and clinical investigations. There are still several issues to be resolved before the comet assay is accepted as a standard assay for detecting DNA damage and repair in a single cell. One of the major issues is the proper quantification of DNA damage/repair. The aim of this article is to develop a new quantitative measure of DNA damage/repair which is represented in the dose-time-response surface. We propose to use the second derivative (2D) of the dose-time-response surface for measuring DNA repair activity. This approach enables us to represent the DNA repair activity of cells exposed to a DNA-damaging agent with a single number by combining all the information of a dose-time-response experiment. The computation procedure includes the application of linear regression. An SAS/AF-based program, "Comet Assay," was developed for this computation and is freely available on the Internet. We considered the response of each of four DNA damage parameters: tail moment, tail length, tail DNA, and tail inertia for constructing the dose-time-response surface. Using data from 25 patients, we observed that 2Ds based on tail moment and tail DNA were highly correlated and that tail inertia might provide information on a somewhat different aspect of DNA damage/repair.