Immunotoxicity of nivalenol after subchronic dietary exposure to rats

Sub-acute oral exposure to lowest observed adverse effect level of nivalenol exacerbates atopic dermatitis in mice via direct activation of mitogen-activated protein kinase signal in antigen-presenting cells

This study investigated the immunotoxic effects of the mycotoxin nivalenol (NIV) using antigen-presenting cells and a mouse model of atopic dermatitis (AD). In vitro experiments were conducted using a mouse macrophage cell line (RAW 264.7) and mouse dendritic cell line (DC 2.4). After cells were exposed to NIV (0.19-5 µmol) for 24 h, the production of pro-inflammatory cytokines (IL-1β, IL-6, and TNFα) was quantified. To further investigate the inflammatory cytokine production pathway, the possible involvement of mitogen-activated protein kinase (MAPK) pathways, such as ERK1/2, p-38, and JNK, in NIV exposure was analyzed using MAPK inhibitors and phosphorylation analyses. In addition, the pro-inflammatory effects of oral exposure to NIV at low concentrations (1 or 5 ppm) were evaluated in an NC/Nga mouse model of hapten-induced AD. In vitro experiments demonstrated that exposure to NIV significantly enhanced the production of TNFα. In addition, it also directly induced the phosphorylation of MAPK, indicated by the inhibition of TNFα production following pretreatment with MAPK inhibitors. Oral exposure to NIV significantly exacerbated the symptoms of AD, including a significant increase in helper T cells and IgE-produced B cells in auricular lymph nodes and secretion of pro-inflammatory cytokines, such as IL-4, IL-5, and IL-13, compared with the vehicle control group. Our findings indicate that exposure to NIV directly enhanced the phosphorylation of ERK1/2, p-38, and JNK, resulting in a significant increase in TNFα production in antigen-presenting cells, which is closely related to the development of atopic dermatitis.

Risk Assessment Considering the Bioavailability of 3-β-d-Glucosides of Deoxynivalenol and Nivalenol through Food Intake in Korea

Deoxynivalenol and nivalenol are major type B trichothecenes and the most frequently occurring mycotoxins worldwide. Their 3-β-d-glucoside forms have recently become a safety management issue. These glucoside conjugates are converted back to the parent toxins during human digestion, but studies to confirm their bioavailability are lacking. In this study, a risk assessment was performed considering the bioavailability of glucoside conjugates. A literature review was conducted to compile the existing bioavailability studies of glucoside conjugates, and three exposure scenarios considering bioavailability were established. As a result of a risk assessment using deterministic and probabilistic methods, both the deoxynivalenol and nivalenol groups had safe levels of tolerable daily intake percentage (TDI%), not exceeding 100%. The TDI% for the nivalenol group was approximately 2-3 times higher than that for the deoxynivalenol group. Notably, infants showed higher TDI% than adults for both toxin groups. By food processing type, the overall TDI% was highest for raw material, followed by simple-processed and then fermented-processed. Since glucoside conjugates can be converted into parent toxins during the digestion process, a risk assessment considering bioavailability allows the more accurate evaluation of the risk level of glucoside conjugates and can direct their safety management in the future.

Fusarium Mycotoxins, Their Metabolites (Free, Emerging, and Masked), Food Safety Concerns, and Health Impacts

The genus Fusarium produces a number of mycotoxins of diverse chemical structures. Fusariotoxins are secondary metabolites produced by toxigenic fungi of the genus Fusarium. The important and commonly encountered fusariotoxins are trichothecenes, fumonisins, and zearalenone. Fusarium mycotoxins pose varying toxicities to humans and/or animals after consumption of contaminated grain. They can cause acute or chronic illness and, in some cases, death. For instance, a range of Fusarium mycotoxins can alter different intestinal defense mechanisms, such as the epithelial integrity, cell proliferation, mucus layer, immunoglobulins, and cytokine production. Of recent concern is the occurrence of emerging and masked Fusarium mycotoxins in agricultural commodities, which may contribute to toxic health effects, although the metabolic fate of masked mycotoxins still remains a matter of scientific discussion. These mycotoxins have attracted attention worldwide because of their impact on human and animal health, animal productivity, and the associated economic losses. In this paper, we review Fusarium mycotoxins and their metabolites with the aim of summarizing the baseline information on the types, occurrence, and health impacts of these mycotoxins in order to encourage much-needed research on integrated management of this unavoidable food contaminant as concerns for food safety continues to grow worldwide.

Immunotoxicity of aflatoxin M1 : as a potent suppressor of innate and acquired immune systems in a subacute study

BACKGROUND

Although, to date, there have been several in vitro and in vivo studies of immunomodulatory effects of aflatoxin M₁ (AFB₁ ), little is known about the effect of AFM₁ on various aspects of innate and acquired immunity. In the present study, AFM₁ was administered intraperitoneally, at doses of 25 and 50 μg kg^-1 , body mass for 28 days and various immunological parameters were measured.

RESULTS

Several parameters related to immune function were suppressed: organ mass, cellularity of spleen, proliferation response to lipopolysaccaride and phytohemagglutinin-A, hemagglutination titer, delayed type of hypersensitivity response, spleen cell subtypes, serum hemolytic activity, serum immunoglobulin G level and cytokine production. AFM₁ did not cause changes in body mass, hematological parameters or the concentration of immunoglobulin M in blood serum.

CONCLUSIONS

Overall, the data suggested that AFM₁ suppressed innate and acquired immunity. Therefore, with respect to consumer safety, it is extremely important to further control the level of AFM₁ in milk, and this should be considered as a precedence for risk management actions. © 2018 Society of Chemical Industry.

Health Risks Associated with Exposure to Filamentous Fungi

Filamentous fungi occur widely in the environment, contaminating soil, air, food and other substrates. Due to their wide distribution, they have medical and economic implications. Regardless of their use as a source of antibiotics, vitamins and raw materials for various industrially important chemicals, most fungi and filamentous fungi produce metabolites associated with a range of health risks, both in humans and in animals. The association of filamentous fungi and their metabolites to different negative health conditions in humans and animals, has contributed to the importance of investigating different health risks induced by this family of heterotrophs. This review aims to discuss health risks associated with commonly occurring filamentous fungal species which belong to genera Aspergillus, Penicillium and Fusarium, as well as evaluating their pathogenicity and mycotoxic properties.

The Effect of Deoxynivalenol on Selected Populations of Immunocompetent Cells in Porcine Blood-A Preliminary Study

Deoxynivalenol (DON) is one of the most prevalent mycotoxins in Europe. Pigs are an animal species that is most susceptible to this mycotoxin. Deoxynivalenol causes significant losses in pig production by lowering feed intake, decreasing daily weight gains, disrupting immune responses, and increasing susceptibility to diseases. The aim of this experiment was to determine the influence of feed contaminated with DON at concentrations insignificantly higher than recommended by the European Commission (900 µg/kg). The experimental feed contained 1008 μg DON/kg. The experiment was performed on eight weaners from the same litter. The animals were randomly divided into two groups: an experimental group (M, n = 4) fed contaminated feed and a control group (C, n = 4) administered feed free of mycotoxins. The experiment lasted for six weeks, and peripheral blood samples were collected from the animals for analyses of selected morphological parameters and changes in the percentages of CD4⁺8-, CD4-8⁺, and CD4⁺8⁺ lymphocytes and antigen-presenting cells (APC) with CD14⁺172⁺ (monocytes), CD172ahigh4-14- (conventional dendritic cells, cDC), and CD172adim4⁺14- (plasmacytoid dendritic cells, pDC) phenotypes. The morphological parameters of porcine blood samples were determined by flow cytometry with non-fluorescent particle-size calibration standards, and no differences were observed between groups M and C. An immunophenotyping analysis of lymphocytes and dendritic cells (DC) revealed an increase in the percentage of CD4⁺8-, CD172ahigh4-14-, and CD172adim4⁺14- cells, and a decrease in the number of CD4-8⁺ cells in group M. The results of this experiment suggest that prolonged exposure to low doses of DON can change the proportions of immunocompetent cells (a shift towards humoral immunity), without affecting their overall counts.

A comparative study on toxicity induced by carbosulfan and malathion in Wistar rat liver and spleen

Organophosphorus (OP) and carbamate (CM) pesticides are widely used in agriculture. These pesticides are highly toxic to humans and their residues in food pose potential threat to human health. In this comparative study, we investigated the effect of subchronic exposure of OPs (malathion, MAL) and CM (Carbosulfan, CB) on rat liver and spleen. Biochemical analysis showed that levels of hepatic enzymes (ALT, ALP, LDH and PAL) changed after exposure to the pesticides. In the liver extracts, lipid peroxidation index increased after the treatment by pesticides. Our results indicated that exposure to MAL and CB leads to alteration of liver redox status. Both pesticides induced focal inflammation and fibrosis in the liver. After subchronic administration of MAL (200 mg/kg) and CB (25 mg/kg), systemic inflammation, as depicted by the increase in IFN-δ activity in liver, was observed in both malathion and carbosulfan treated animals. In addition, the results showed that MAL significantly increased TCD4+ and TCD8+ lymphocyte number. It also decreased INF-δ and IL-4 production. However, CB induced a reduction of TCD8+ number and cytokine production in spleen cells. In conclusion, malathion and carbosulfan had significant immunomodulatory properties in the spleen with inflammation and oxidative stress induction in the liver.

Association of inflammatory response and oxidative injury in the pathogenesis of liver steatosis and insulin resistance following subchronic exposure to malathion in rats

Insulin resistance and risk of type 2 diabetes are the most important complications following exposure to organophosphorous (OPs) pesticides. Regarding the importance of liver on metabolic pathways regulation, in particular blood glucose homeostasis, we focused on liver inflammation and oxidative damages in a subchronic model of toxicity by malathion. Adult male Wistar rats of body weight 200-250g were used for the study. Malathion (200mg/kg b.w./day) was administered to rats by oral intubation for 28 days. Glycemic and insulin resistance indices, markers of liver injury, markers of inflammation and oxidative stress were assessed. Malathion-treated rats showed increased glycemia, insulinemia and glycated hemoglobin level, HOMA-IR and HOMA-β indices, plasma activities of hepatocellular enzymes, lipid peroxidation index, CD3(+)/CD4(+) and CD3(+)/CD4(+) and pro-inflammatory cytokines when decreased antioxidant status in liver was noted. Most of our study indicates that malathion promotes insulin resistance, inflammation and Hepatosteatosis in subchronic model of exposure. On the basis of biochemical and molecular findings, it is concluded that insulin resistance induced by malathion occurs through oxidative stress and related pro-inflammatory markers in a way to result in a reduced function of insulin in liver cells.

Antioxidant and anti-inflammatory effects of N-acetylcysteine against malathion-induced liver damages and immunotoxicity in rats

AIMS

Occupational exposure to organophosphate pesticides is becoming a common and increasingly alarming world-wide phenomenon. The present study is designed to investigate the preventive effect of N-acetylcysteine on malathion-induced hepatic injury and inflammation in rats.

MAIN METHODS

Adult male Wistar rats of body weight 200-230 g were used for the study. Malathion (200mg/kg b.w./day) was administered to rats by oral intubation and N-acetylcysteine (2g/l) in drinking water for 28 days. Rats were sacrificed on the 28th day, 2h after the last administration. Markers of liver injury (aspartate transaminase, alanine transaminase, alkaline phosphatase and lactate desyhdogenase), inflammation (leukocyte counts, myeloperoxidase, immunophenotyping of CD4(+) and CD8(+), interleukin-1β, interleukin-6 and interferon-γ expression) and oxidative stress (lipid peroxidation, reduced glutathione and antioxidant status) were assessed.

KEY FINDINGS

Malathion induced an increase in activities of hepatocellular enzymes in plasma, lipid peroxidation index, CD3(+)/CD4(+) and CD3(+)/CD4(+) percent and pro-inflammatory cytokines, when decreased antioxidant status in liver was noted. When malathion-treated rats were compared to NAC supplemented rats, leukocytosis, T cell count and IL-1β, IL-6, INF-γ expression were reduced. Furthermore, NAC restored liver enzyme activities and oxidative stress markers.

SIGNIFICANCE

Malathion induces hepatotoxicity, oxidative stress and liver inflammation. N-acetylcysteine showed therapeutic effects against malathion toxicity.

The Kidneys of Infant Mice are not Sensitive to the Food Mycotoxin Contaminant Nivalenol

Nivalenol (NIV) is a trichothecene mycotoxin produced by Fusarium fungi that frequently contaminates agricultural commodities. Dietary administration of NIV to adult mice affects the renal glomeruli, but data about NIV toxicity in human infants are limited. To evaluate the effects of NIV on infant kidneys, 3-week-old male ICR-derived glomerulonephritis (ICGN) and ICR mice were administered 0, 4, 8 or 16 ppm NIV in diet for 4 weeks, and their renal status was compared with age-matched or adult ICR mice. In ICGN mice, the number of glomeruli showing mesangial expansion and α-smooth muscle actin (SMA)-positive mesangial cells was higher with 16 ppm NIV compared with controls. No other significant differences were observed in ICGN mice. In infant ICR mice, the IgA serum concentrations were significantly elevated without glomerular morphological changes in the 16 ppm NIV group. There was no difference in NIV sensitivity in the kidneys of infant ICGN and ICR mice. These data suggest that the kidneys in infant mice are not sensitive to nivalenol under the present conditions.

The immunomodulatory effects induced by dietary Zearalenone in pregnant rats

CONTEXT

Zearalenone (ZEN) is a common contaminant that is present in feedstuff of high humidity and high temperatures.

OBJECTIVE

The aim of this study was to investigate the effects of diets contaminated with different concentrations of ZEN on immunomodulation in early pregnant rats.

MATERIALS AND METHODS

Forty-eight pregnant Sprague Dawley (SD) rats were randomly divided into four treatment groups fed on a diet supplemented with one of four concentrations of ZEN: 0 mg/kg (ZEN 0), 50 mg/kg (ZEN 50), 100 mg/kg (ZEN 100) and 150 mg/kg (ZEN 150). The pregnant rats were fed ZEN-treated diets from gestation days 0 to 7 and a basal diet from gestation days 8 to 20.

RESULTS

ZEN exposure (ZEN 100 and 150) caused significant decreases in splenic coefficients, viability of splenocyte and T-cell proliferation and induced histopathological damage in the spleen of early pregnant rats compared with other groups. Levels of IgG and IgA were decreased, while IgM was increased, in high doses of ZEN (ZEN 100 and ZEN 150) compared with other groups. ZEN 150 caused increases in white blood cells and hemoglobin and induced a significant decrease in platelets in blood of the pregnant rats compared with other groups. ZEN 150 increased the mRNA expression levels of interleukin (IL)-6, IL-18 and IL-1β and decreased the mRNA expression levels of interferon-γ, tumor necrosis factor-α and IL-10 in the spleen of pregnant rats compared with ZEN 0.

CONCLUSION

High doses of ZEN-induced immunomodulatory effects on early pregnant rats by altering immunological parameters.

Structural determination of a nivalenol glucoside and development of an analytical method for the simultaneous determination of nivalenol and deoxynivalenol, and their glucosides, in wheat

Trichothecene mycotoxins such as nivalenol and deoxynivalenol frequently contaminate foodstuffs. Recently, several trichothecene glucosides have been found in trichothecene-contaminated foods, and information about their chemistry, toxicity, and occurrence is required. In this study, a glucoside of nivalenol was isolated from nivalenol-contaminated wheat and was identified as nivalenol-3-O-β-D-glucopyranoside. Analytical methods using a multifunctional column or an immunoaffinity column have been developed for the simultaneous determination of nivalenol, nivalenol-3-O-β-D-glucopyranoside, deoxynivalenol, and deoxynivalenol-3-O-β-D-glucopyranoside in wheat. The methods were validated in a single laboratory, and recovery from wheat samples spiked at four levels ranged between 86.4 and 103.5% for the immunoaffinity column cleanup. These mycotoxins in contaminated wheat samples were quantitated by the validated method. Nivalenol-3-O-β-D-glucopyranoside was detected in the nivalenol-contaminated wheat, and the percentage of nivalenol-3-O-β-D-glucopyranoside to nivalenol ranged from 12 to 27%. This result indicates that the analytical method developed in this study is useful for obtaining data concerning the state and level of food contamination by nivalenol, deoxynivalenol, and their glucosides.

Applications of flow cytometry to toxicological mycotoxin effects in cultured mammalian cells: a review

This review gives an overview of flow cytometry applications to toxicological studies of several physiological target sites of mycotoxins on different mammalian cell lines. Mycotoxins are secondary metabolites of fungi that may be present in food, feed, air and water. The increasing presence of mycotoxins in crops, their wide distribution in the food chain, and their potential for toxicity demonstrate the need for further knowledge. Flow cytometry has become a valuable tool in mycotoxin studies in recent years for the rapid analysis of single cells in a mixture. In toxicology, the power of these methods lies in the possibility of determining a wide range of cell parameters, providing valuable information to elucidate cell growth and viability, metabolic activity, mitochondrial membrane potential and membrane integrity mechanisms. There are studies using flow cytometry technique on Alternaria, Aspergillus, Fusarium and Penicillium mycotoxins including information about cell type, assay conditions and functional parameters. Most of the studies collected in the literature are on deoxynivalenol and zearalenone mycotoxins. Cell cycle analysis and apoptosis are the processes more widely investigated.

Protective Effect of Stachybotrys microspora Triprenyl Phenol-7on the Deposition of IgA to the Glomerular Mesangium in Nivalenol-induced IgA Nephropathy Using BALB/c Mice

Activators of tissue proteolysis including Stachybotrys microspora triprenyl phenol (SMTP)-7 are a new class of agents that are expected to be effective for amelioration of chronic tissue destructive diseases. The present study was performed to examine whether SMTP-7 is effective for the amelioration or protection of early-stage IgA nephropathy (IgAN) induced by nivalenol (NIV) in female BALB/c mice. In Experiment 1, mice were administered NIV at 24 ppm in diet for 8 weeks, and during the NIV treatment, they were intraperitoneally injected with SMTP-7 (10 mg/kg) three times a week. In Experiment 2, mice were injected similarly with SMTP-7 during the last 4 weeks of a 16-week NIV treatment. Immunofluorescence analysis revealed an inhibitory effect of SMTP-7 on the glomerular deposition of IgA in Experiment 1; however, it was ineffective in Experiment 2. On the other hand, SMTP-7 did not affect the serum concentration of IgA in both experiments. These results suggest that SMTP-7 has a potential to decrease the progression of IgAN induced by NIV through inhibition of local accumulation of IgA in the glomerular mesangium, while it was ineffective for suppression of IgA production. On the other hand, SMTP-7 was found to be ineffective for already deposited IgA, suggesting that SMTP-7 may not be effective for ameliorating advanced IgAN.

Haematological and immunological effects of repeated dose exposure of rats to integerrimine N-oxide from Senecio brasiliensis

This study is the first in the literature to focus attention on the possible immunotoxic effect of integerrimine N-oxide content in the butanolic residue (BR) of Senecio brasiliensis, a poisonous hepatotoxic plant that contains pyrrolizidine alkaloids (PAs). PAs have been reported as a pasture and food contaminant and as herbal medicine used worldwide and are responsible for poisoning events in livestock and human beings. After the plant extraction, BR extracted from Senecio brasiliensis was found to contain approximately 70% integerrimine N-oxide by elemental and spectral analyses ((1)H and (13)C NMR), which was administered to adult male Wistar Hannover rats at doses of 3, 6 and 9 mg/kg for 28 days. Body weight gain, food consumption, lymphoid organs, neutrophil analysis, humoural immune response, cellular immune response and lymphocyte analysis were evaluated. Our study showed that integerrimine N-oxide could promote an impairment in the body weight gain, interference with blood cell counts and a reducing T cell proliferative activity in rats; however, no differences in the neutrophil activities, lymphocytes phenotyping and humoural and cellular immune responses were observed. It is concluded that doses of integerrimine N-oxide here employed did not produce marked immunotoxic effects.

Toxicological mechanisms and potential health effects of deoxynivalenol and nivalenol

Produced by the mould genus Fusarium, the type B trichothecenes include deoxynivalenol (DON), nivalenol (NIV) and their acetylated precursors. These mycotoxins often contaminate cereal staples, posing a potential threat to public health that is still incompletely understood. Understanding the mechanistic basis by which these toxins cause toxicity in experimental animal models will improve our ability to predict the specific thresholds for adverse human effects as well as the persistence and reversibility of these effects. Acute exposure to DON and NIV causes emesis in susceptible species such as pigs in a manner similar to that observed for certain bacterial enterotoxins. Chronic exposure to these mycotoxins at low doses causes growth retardation and immunotoxicity whereas much higher doses can interfere with reproduction and development. Pathophysiological events that precede these toxicities include altered neuroendocrine responses, upregulation of proinflammatory gene expression, interference with growth hormone signalling and disruption of gastrointestinal tract permeability. The underlying molecular mechanisms involve deregulation of protein synthesis, aberrant intracellular cell signalling, gene transactivation, mRNA stabilisation and programmed cell death. A fusion of basic and translational research is now needed to validate or refine existing risk assessments and regulatory standards for DON and NIV. From the perspective of human health translation, biomarkers have been identified that potentially make it possible to conduct epidemiological studies relating DON consumption to potential adverse human health effects. Of particular interest will be linkages to growth retardation, gastrointestinal illness and chronic autoimmune diseases. Ultimately, such knowledge can facilitate more precise science-based risk assessment and management strategies that protect consumers without reducing availability of critical food sources.

In ovo exposure of a Fusarium mycotoxin butenolide induces hepatic and renal oxidative damage in chick embryos, and antioxidants provide protections

Butenolide is a mycotoxin produced by several toxigenic Fusarium species. It frequently invades many important grains, and evokes a broad spectrum of toxic effects. For these reasons, butenolide poses a health risk to both humans and animals. However, many toxicology issues of butenolide including targets and mechanisms of toxicity remain to be elucidated so far. The present study therefore attempts to reveal the toxic profile of butenolide from a viewpoint of oxidative damage, using chick embryos as an in vitro model. A single in ovo injection of butenolide resulted in significant oxidative injuries in embryonic livers and kidneys, as manifested by a dose-dependent depletion of sulfhydryl groups, reduction of glutathione peroxidase activity, and increase of thiobarbituric acid reactive substances production, an indicator of lipid peroxidation. In contrast, co-injections of butenolide with antioxidants sodium selenite, vitamin C and a representative antioxidative enzyme superoxide dismutase markedly abated these oxidative toxicities. In conclusion, the present study suggests that oxidative damage may serve as a mediator in the toxicity of butenolide, and amelioration of antioxidant defense capacity by exogenous supplementation may play a role in the prevention and treatment of butenolide intoxication.

Effects of prometryne on apoptosis and necrosis in thymus, lymph node and spleen in mice

Prometryne is a methylthio-s-triazine herbicide. Significant traces are documented in environment, mainly waters, soil and plants used for nutrition. The aim of this study was to estimate prometryne immunotoxic properties through induction of apoptotic and/or necrotic changes in thymocytes, splenocytes and lymph node cells after repeated subchronical exposure. Three different doses of prometryne (185, 375, 555mgkg(-1)) were applied per os every 48h, over 28 days. Flow cytometry assay (annexinV-FITC and PI) was conducted to record apoptotic and necrotic damage. In the spleen significant changes in the percentage of apoptotic cells were not detected between treated and control groups respectively. In thymus and lymph node, within the lowest dose group (185mgkg(-)1), an increase in percentage of early apoptosis without any significant increase in necrosis was detected. Medium (375mgkg(-1)) as well as high dose triggered increase in late apoptosis in lymph node while in thymus; late apoptosis was increased only in animals exposed to the highest dose (555mgkg(-1)). The highest applied dose, in thymus and lymph node respectively, caused a general decrease in percentage of vital cells in favour of marked increase of percentages of all types of dying cells (apoptotic, late apoptotic/early necrotic and necrotic). Prometryne caused disbalance in major organs of immune system, markedly lymph nodes and thymus, by induction of early apoptotic changes in dose/time specific manner.

Nivalenol and the targeting of the female reproductive system as well as haematopoietic and immune systems in rats after 90-day exposure through the diet

Nivalenol (NIV) is considered to be an important trichothecene mycotoxin produced by Fusarium species because of its frequent contamination in wheat and barley worldwide. The present study examined the subchronic toxicity of NIV in male and female F344 rats fed diets containing 0, 6.25, 25 and 100 mg kg(-1) of the toxin for 90 days. During the experimental period there was a decrease in the white blood cell count at 100 mg kg(-1) in males and at > or =6.25 mg kg(-1) in females. Histopathologically, treatment-related changes were observed in the haematopoietic and immune systems in both sexes and in the female reproductive system at 100 mg kg(-1). Flow cytometric analysis of splenic cells revealed an elevation in the ratio of helper/cytotoxic T-lymphocytes at 100 mg kg(-1). In summary, NIV targets the female reproductive system as well as haematopoietic and immune systems in rats fed NIV for 90 days. Based on a significant decrease in white blood cells in female rats relative to controls, the lowest observable effect level was calculated as 0.4 mg kg(-1) body weight day(-1).