Effects of apple peels extracts on immunoglobulin and other biochemical parameters in rats fed on high dose of nitrate and nitrite

Dietary nitrate has been implicated in the formation of methemoglobin and carcinogenic nitrosamines in humans. The present study conducted to investigate the effects of apple peels extracts on lowering the deleterious effect of nitrate and nitrite. Various nutritional, immunological and biochemical parameters were estimated. Apple peels [ethanol or methanol] 1% extracts was added to the high dose of nitrate or nitrite in rats diet. KNO3 used as nitrate compound at 0.2% and NaNO2 used as nitrite compound at 0.05% for 8 weeks. The results indicated that the presence of either nitrate or nitrite in rat diet caused a significant decrease in food intake, body weight gain [BWG], food and protein efficiency ratio [FER, PER] when compared with control group. It could be observed that the values of immunoglobulins [lgG and 1gM], hemoglobin [Hb] and hematocrit [HCT] were significantly decreased in rats fed on basal diet with nitrate or nitrite without added apple peels extract p

effect of storage on the level of nitrite and nitrate in meat products available in Cairo market and effect of adding some antioxidants on one of the meat products

Meat is considered of high nutritional value as it contain protein, fat, vitamins and minerals. Nitrates and nitrites were used in meat products. The presence of nitrates and nitrites in foods may play a negative role in general health status. This study aimed to estimate the concentration levels of nitrite and nitrate in different meat and meat products that are available in Cairo Governorate markets and the effect of adding some antioxidant on the level of nitrates and nitrites in the products. The nitrate and nitrite contents were determined according to Griess methods. The results indicated that, sausage and kofta fresh samples tended to have the highest content of sodium nitrates, followed by burger. On contrast, luncheon fresh samples tended to have the lowest content of nitrates. As expected, after 30 and 60 days of storage, the level of nitrates has been significantly decreased, as compared to fresh samples. On contrast, the level of nitrites has been significantly increased, as compared to fresh samples. The investigated samples contained nitrite lower than the recommended safety limit proposed by Egyptian standards. With the exception of basterma samples the contained nitrites were higher than the recommended by Egyptian standard partially after storage. It should be noticed that, all investigated sausage samples treated with antioxidant [vitamin C, vitamin E and selenium] have nitrites in the amount lower than the recommended safety limit, even after storage for 60 days. All tested antioxidants had a good affect for lowering nitrate and nitrite contents for all investigated samples. It should be noted that vitamin C tended to have the most effect for reducing nitrites among all tested antioxidants followed by vitamin E

Nitratos, nitritos, nitrosaminas e seus efeitos sobre o organismo humano / Nitrates, nitrites, nitrosamines and their effects on the human body

Os nitratos e nitritos, na forma de sal de sódio e potássio, são largamente usados no processamento de derivados cárneos, originando produtos como presuntos, bacon e salsichas. São conservantes geralmente adicionados aos sais de cura, sendo responsáveis pela formação e estabilidade da cor de produtos cárneos, possuindo também atividade antimicrobiana. O nitrito pode ser adicionado diretamente na carne ou ser obtido através da redução do nitrato na própria carne, por ação de bactérias redutoras. Os nitratos são pouco tóxicos, a não ser em níveis elevados, porém, os nitritos possuem uma toxicidade maior, pois são capazes de se combinar com compostos presentes nos alimentos formando compostos nitrosos denominados nitrosaminas. Como a maioria desses compostos têm apresentado atividade cancerígena e mutagênica, a sua formação e ocorrência estão sendo cada vez mais estudadas com o propósito de se conhecer melhor esse tipo de contaminante e os riscos potencialmente envolvidos com a sua ingestão. A utilização destes conservantes em concentrações adequadas e rigorosamente controladas, associada com a avaliação da sua ingesta pela população, possibilita minimizar a possibilidade de ocorrência de problemas de toxidade pelo seu consumo. Com isso tem-se uma maneira de diminuir os riscos sofridos pelos consumidores de produtos cárneos curados.

Concentração de nitrito endometrial e a ocorrência de patologias uterinas em vacas / Endometrial nitrite concentration and the occurrence of uterine pathologies of cows

Relacionou-se a concentração de nitrito com a ocorrência de enfermidades uterinas. Lavado intrauterino de 1ml de PBS foi realizado em 25 peças uterinas de vacas vazias para mensuração da concentração de nitrito pela reação de Griess. Elevada concentração de nitrito exibiu relação significativa com distrofia angiomatosa (157,57±108,80mM), endometrite (102,96±87,58mM) e fibrose periglandular (99,15±89,75mM); e não significativa com e hiperplasida endometrial cística (94,07±18,89mM) e adenomiose (77,40±81,25mM). Contudo, elevada concentração de nitrito mostrou relação significativa com adenomiose acentuada profunda pelo teste t. Os resultados indicam que a síntese de óxido nítrico está elevada nessas enfermidades.

The occurrence of uterine pathologies was evaluated considering uterine nitrite concentration. The uterus of 25 non pregnant cows was washed with 1ml of PBS to measure the nitrite concentration using the Griess reaction . There was significant relationship between high nitrite concentration with angiomatosis dystrophy (157,57 ±108,80mM), endometritis (102,96±87,58mM) and periglandular fibrosis (99,15±89,75mM). No relation was found between nitrite concentration and cystic endometrial hyperplasia (94,07±18,89mM) and adenomyosis (77,40±81,25mM). However, high nitrite concentration showed a significant relationship with deep accentuate adenomyosis by t test. The data suggest that nitric oxide synthesis is elevated in these illnesses.

Comparison between biochemical responses of the teleost pacu and its hybrid Tambacu (Piaractus mesopotamicus xColossoma macropomum) to short term nitrite exposure

Aquatic environmental factors are very changeable in short periods. Among these factors are pH, temperature, dissolved oxygen, ammonia and ions. Nitrite, as one ion naturally present in aquatic systems, deserves particular consideration as it is highly toxic for many species. Among fish, nitrite may have harmful effects, such as methemoglobin (MtHb) formation, disruption to the gill and hepatic structure, which could result in hemolytic anemia and cell hypoxia by reducing the functional hemoglobin content. In this work, we compared hematological and metabolical responses of pacu and its hybrid tambacu exposed to 20 ppm of environmental nitrite. It was observed that the MtHb content was less than 18 percent in tambacu while pacu reached nearly 8 percent. These data reflect specific differences in nitrite uptake by the gill. The hematocrit of both fish was distinct; pacu did not have a typical response of poisoning by nitrite. This fact shows less skill of the hybrid to cope with environmental nitrite. Incipient hemolytic anemia was observed in pacu and both species presented a neoglycogenic profile. The glucose-provider character of the liver was more evident in tambacu. The white muscle of both species presented distinct metabolic behavior. While in pacu the white muscle was predominantly oxidative, in tambaqui the lactic fermentation was the most important metabolic profile. Metabolic and hematological observations in both species show that they present distinct metabolical strategies to cope with toxic effects of nitrite and there is no evidence that the hybrid is more resistant to nitrite.

Os fatores ambientais nos meios aquáticos são muito flutuantes em curtos intervalos de tempo. Valores de pH, temperatura, oxigênio dissolvido, amônia e íons podem estar freqüentemente variando. Entre esses íons, o nitrito merece especial atenção por ser altamente tóxico para muitas espécies. Entre os peixes, o nitrito pode apresentar efeitos danosos como a formação de metahemoglobina (MtHB), lesão às estruturas branquiais e hepática, podendo levar a quadros de anemia hemolítica e hipóxia celular pela redução do teor de hemoglobina funcional. Neste trabalho, foram comparadas as respostas hematológicas e metabólicas do pacu e de seu híbrido tambacu expostos a 20 ppm de nitrito ambiental, e verificou-se que o teor de MtHb no tambacu foi menor que 18 por cento, enquanto no pacu atingiu valores de 8 por cento. Esses valores refletem diferenças específicas na captação de nitrito pelas brânquias. O hematócrito de ambas as espécies foi diferente; o pacu não apresentou uma resposta típica à intoxicação pelo nitrito. Este fato revelou uma diminuição na capacidade do híbrido em resistir ao nitrito ambiental. Observou-se no pacu um princípio de anemia hemolítica. As duas espécies mostraram um perfil bioquímico neoglicogênico. O papel glicemiante do fígado foi mais evidente no tambacu. O músculo branco de ambas as espécies mostrou um comportamento metabólico distinto. Enquanto o músculo do pacu foi predominantemente oxidativo, o músculo branco do tambaqui exposto ao nitrito realizou fermentação láctica. As observações metabólicas e hematológicas em ambas as espécies indicam que estas apresentam estratégias metabólicas diferentes para enfrentar os efeitos tóxicos do nitrito ambiental, não sendo evidenciada qualquer vantagem do híbrido neste particular.

Efeito do uso de nitrato e nitrito na inibição de Clostridium perfringens tipo A em linguiça bovina curada / The effect of the use of nitrate and nitrite on the inibition of Clostridium perfringnes type on the bovine cured sausage

O presente trabalho teve como objetivo verificar a eficiência dos conservantes nitrato e nitrito na inibição do Clostridium perfringens tipo A, (responsável por toxinfecção alimentar) durante a vida útil de linguiças de carne bovina curadas. As amostras foram elaboradas partindo-se de massa subdividida em grupo controle e grupo tratamento (adicionado de sal de cura), ambos inoculados com a cultura de C. perfringens (6 x 10 UFC). Efetuaram-se análises microbiológicas para quantificação da bactéria e a determinação dos níveis residuais de nitrato e nitrito. Os resultados demonstraram que durante o período de vida útil do produto( 44 dias) não houve desenvolvimento do microorganismo nas linguiças que receberam tratamento , mesmo em níveis baixos de nitrato e nitrito. Já no grupo controle verificou-se crescimento do microorganismo, embora enquadrado no limite exigido pela legislação brasileira (3 x 10 UFC). As quantidades de nitrato e nitrito de sódio adicionadas (200ppm) indicaram período de redução dos níveis de no mínimo quatro dias após o processo de elaboração, permanecendo então abaixo dos limites permitidos pela legislação (150ppm). Os resultados obtidos evidenciaram a efici~encia dos conservantes nitrato e nitrito na inibição do microorganismo Clostridium perfringens tipo A em linguiça

Determinações espectrofotométricas de nitrito e nitrato em sais de cura / Spectrophotometrics determination of nitrite and nitrate in curing salts

Este trabalho objetivou desenvolver um método para determinar espectrofotométricamente nitrito e nitrato em sais de cura. Foram estudados espectros de absorção do nitrato em faixa do ultravioleta, comparação de medidas no ultravioleta de nitrato e nitrito, usando cubetas de quartzo e metacrilato, e determinações de nitrito e nitrato em sais de cura nas regiões visível e ultravioleta. Com relação às determinações no ultravioleta, máxime no que diz respeito ao nitrato, verificou-se máxima absorção do nitrato na faixa de 301 nm; as cubetas de quartzo e de metacrilato apresentam as mesmas respostas espectofotométricas; e não existem diferenças estatísticas significativas nos métodos espectrofotométricos nas regiões visível e ultravioleta ás determinações de nitrito e de nitrato em sais de cura (P<0,0001). Com base nesses ensaios, concluímos que o método espectrofotométrico visível para determinação de nitrato possui inúmeras etapas que podem gerar erros, além do manuseio do cádmio metálico que é um produto altamente tóxico para o ser humano e para o meio ambiente; entretanto, o método espectrofotométrico direto (UV) é rápido e preciso.

Determinações espectrofotométricas de nitrito e nitrato em sais de cura / Spectrophotometrics determination of nitrite and nitrate in curing salts

Este trabalho objetivou desenvolver um método para determinar espectrofotométricamente nitrito e nitrato em sais de cura. Foram estudados espectros de absorção do nitrato em faixa do ultravioleta, comparação de medidas no ultravioleta de nitrato e nitrito, usando cubetas de quartzo e metacrilato, e determinações de nitrito e nitrato em sais de cura nas regiões visível e ultravioleta. Com relação às determinações no ultravioleta, máxime no que diz respeito ao nitrato, verificou-se máxima absorção do nitrato na faixa de 301 nm; as cubetas de quartzo e de metacrilato apresentam as mesmas respostas espectofotométricas; e não existem diferenças estatísticas significativas nos métodos espectrofotométricos nas regiões visível e ultravioleta ás determinações de nitrito e de nitrato em sais de cura (P<0,0001). Com base nesses ensaios, concluímos que o método espectrofotométrico visível para determinação de nitrato possui inúmeras etapas que podem gerar erros, além do manuseio do cádmio metálico que é um produto altamente tóxico para o ser humano e para o meio ambiente; entretanto, o método espectrofotométrico direto (UV) é rápido e preciso.

The aim of this work was to develop a method of measuring spectrophotometrically nitrite and nitrate in curing salts.The folowing parameters have been studied: nitrate absorption spectra in the ultraviolet range, comparison of the nitrate and nitrite measures at the ultraviolet range using quartz and methacrylate cuvettes, and the nitrite and nitrate determinations in curing salts at the visible and ultraviolet ranges. With regard to the ultraviolet range determinations,it has been verified that the maximum nitrate absorption occurred in the 301nm zone, quartz and methacrylate cuvettes showed similar spectrophotometrics values, and there are no significant statistical differences in spectrophotometrics methods between the visible and ultraviolet ranges concerning nitrite and nitrate determinations in curing salts (P<0,0001). Based on these assays, it has been concluded that the visible spectrophotometric method to determine nitrate has severa1 steps that might lead the analyst to make mistakes, in addition there is the fact that the metallic cadmium handling can be harmful, due to its toxic properties to human beings and to theenvironment as well. Nevertheless, the direct (UV) spectrophotometric method proved to be fast and accurate.

Level of nitrate and nitrite contents in drinking water of selected samples received at AFPGMI, Rawalpindi

Contamination of drinking water by nitrates is an evolving public health concern since nitrate can undergo endogenous reduction to nitrite and nitrosation of nitrites can form N-nitroso compounds, which are potent carcinogens. The carcinogenic feature of N-nitroso compounds has been well established. Nitrites can lead among infants to the disease called methemoglobinemia [blue baby syndrome]. There is a strong relationship between nitrate concentration and recurrent diarrhoea and also other illnesses. The aim of this study was to evaluate the level of nitrate and nitrite contents in some drinking water samples. In this study we analysed 162 water samples received at Water Quality Control Laboratory, AFPGMI, Rawalpindi for their nitrate and nitrite contents. Out of these 162 water samples, 153 [94%] and 133 [82%] samples had nitrate and nitrite contents in varying concentrations, while 64 [40%] and 22 [14%] had nitrate and nitrite concentrations more than Pakistani standards. Given the potential health risk associated with the presence of toxicants like nitrates and nitrites in water sources used for drinking yet the scarcity of available data, there is a need to evaluate these waters and develop strategies to reduce and prevent their contamination

The toxicity of ammonia, nitrite and nitrate to the fish, Catla catla (Hamilton).

The acute toxicity of unionized ammonia; nitrite and nitrate to the Indian major carp Catla catla (Hamilton) was determined using static and continuous flow through systems for 24 hours. The median lethal concentration (LC50) values for 24 h of ammonia (NH3-N), nitrite (NO2-N) and nitrate (NO3-N) were 0.045 mg/l, 120.84 mg/l and 1565.43 mg/l in static test respectively and were 0.036 mg/l, 117.43 mg/l and 1484.08 mg/l in continuous flow through test respectively.

Metabolic responses of the teleost Hoplias malabaricus to high levels of environmental nitrite

The metabolic responses of Hoplias malabaricus to hypoxia caused by nitrite exposure was studied and compared to previous data of hypoxia caused by low environmental oxygen concentrations. These metabolic responses were analyzed from the contents of glycogen, glucose, lactate and pyruvate in liver, red and white muscle, heart and plasma. Glycogen mobilization provided clues to explain the metabolic behavior of the organism against internal hypoxia. The ratio of closely related metabolic intermediates was used to analyze its reaction displacement. The results permit us to conclude that H. malabaricus responds to nitrite hypoxia in the same way as when exposed to low oxygen external levels. That means hydrolyxis of hepatic glycogen followed by its synthesis in white muscle. Metabolism in the heart muscle seems to be more intense than in red muscle. Although internal and external hypoxia presented similar metabolic responses, the signiificance of this strategy remains uncertain.

Algunos aspectos epidemiológicos del cáncer gástrico y su relación con helicobacter pylori en Chile / Some epidemiological factors of gastric cancer and it relation with helicobacter pylori in Chile

El patógeno bacteriano mas común del tracto gastrointestinal en el ser humano es el Helicobacter pylori, un microorganismo que produce inflamación de la mucosa gástrica, que en un subgrupo de individuos facilita la progresión de la ulceración. Ciertos factores ambientales, como alto consumo de nitratos y determinados factores genéticos pueden estar involucrados en la progresión de la inflamación a displasia. En Chile, mas de la mitad de los adolescentes y un alto porcentaje de niños son seropositivos a H. pylori

Food-borne nitrates and nitrites as a cause of methemoglobinemia.

Methemoglobinemia is a potentially fatal condition. Previous reports of toxic methemoglobinemia due to food-borne nitrates and nitrites are reviewed. Contamination of food during manufacture or degradation of nitrates in vegetables appear to be the most important factors. Some food items, such as refrigerated "dim-sum", stuffed pork and Chinese sausages, are very popular among some Asian populations; a stringent control against the excessive use of nitrates and nitrites is required in order to prevent outbreaks of toxic methemoglobinemia. Patients with glucose-6-phosphate dehydrogenase deficiency, a common condition in some Asian populations, may present with methemoglobinemia and intravascular hemolysis following exposure to oxidant drugs or chemicals. Methylene blue is inefficient and may exacerbate hemolysis in these patients; partial exchange transfusion may be required.

Are the nitrites and nitrates responsible for the carcinoma in the operated stomach?

The carcinogenesis of the operated stomach has been attributed to several etiologies: bilio-pancreatic reflux, achlorhydria, hypochlorydria, atrophic gastritis, atypical bacteria, food and environmental factors, nitrites, nitrates, N-nitroso compounds, the two different types of epitelium in the suture line and other. Seventy two male WISTAR rats (300-380 g) were employed, divided into 2 groups and observed during 8 months, drinking water only or aqueous solution of potassium nitrite plus potassium nitrate (30 mg/kg/day). Each group was subdivided into other 4 groups with 9 animals, submitted to gastrotomy (GT) (control group), gastrojejunostomy plus truncal vagotomy (GJ + TV), BILLROTH II gastrectomy plus truncal vagotomy (BII + TV) and Roux-en-Y gastrectomy plus truncal vagotomy (RY + TV). After the observation period, the animals were sacrificed and performed histopathological studies of the operated stomachs. The results showed that the animals that ingested nitrite + nitrate solutions presented significative findings of cystic gladular hyperplasia (41,5 per cent), dysplasia (19,6 per cent) and carcinoma (5,6 per cent). Carcinomas were found in the animals submitted to GJ + TV and BII + TV. The authors concluded that the ingestion of nitrite and nitrate causes important modifications into the mucosa of the gastric stump, however more studies are needed to clarify the mechanisms of carcinogenesis in the operated stomach.

Nitratos y nitritos y su posible relación con la morbilidad por cáncer de esófago o estómago / Nitrates and nitrites and their possible relationship with morbidity of esophageal or stomach cancer

Se realizó un estudio retrospectivo en 74 pacientes con cáncer de esófago o estómago residentes en Ciudad de La Habana y reportados al Registro Nacional de Cáncer, para buscar posibles asociaciones entre la frecuencia del consumo de productos con contenidos diversos de nitratos y nitritos y la aparición de cáncer en dichos órganos. Mediante una encuesta se recogió información acerca del nivel educacional, el ingreso per cápita, el consumo de bebidas alcohólicas, productos ahumados, embutidos, vegetales y viandas, así como el hábito de fumar y otras variables. Se utilizó para el análisis estadístico la prueba de chi-cuadrado, razón de disparidad y sus límites de confianza. No se encontraron diferencias significativas entre los casos y los controles en la frecuencia de consumo de ninguno de los grupos de alimentos de acuerdo con los niveles de riesgo establecidos. Tampoco se encontró relación entre los otros factores de riesgo asociados y la morbilidad por cáncer de estas localizaciones

Intoxicación por nitratos y nitritos / Poisming by nitrate and nitrite

En esta revisión los aspectos más inportantes sobre la intoxicación por nitratos y nitritos, a propósito de la presentación de un caso en Venezuela. Se han publicado varios casos de intoxicación por nitrato de sodio y nitrito de amonio, unos de forma accidental y otros por ingesta intencional exposción industrial. Los síntomas que frecuentemente se presentan son: hipotensión (asociada o no a síncope); taquipnea; cianosis; convulsiones; coma y en casos severos muerte

Nitrates and nitrites pollution in cheese and concentrated milk

Twenty five different cheese samples and ten concentrated milk samples were randomly collected from different localities of Zagazig City. Sharkia Governorate. The collected samples were analysed colorimetrically for nitrates and nitrites by using spectrophotometer. The obtained results revealed that the average concentration of nitrates was 86.61, 123.92 and 130.86 mg/kg in skimmed milk, Domiati and full cream soft cheeses samples respectively, while processed and hard cheese samples contained an average concentration of 50.21 and 26.58 mg/kg respectively. The average concentration of nitritesis, skimmed milk, domiati and full cream soft cheese was 1.77, 2.014 and 1.64 mg/kg respectively. Meanwhile, processed and hard cheese exhibited nitrites with an average concentration of 0.81 and 4.27 mg/kg. The examined milk powder and condensed milk samples having an average concentration of 150.62 and 146.32 mg/kg for nitrates, while nitrites was 1.04 and 1.79 mg/kg in milk powder and condensed milk. The most analysed samples contained nitrates above the desirable limit [50 mg/kg] recommended by and Stephany et al. [1978] and Bertelsen [1979]. In contrast nitrites were within the desirable limit [2 mg/kg] in most of the analysed samples with the exception of domiati and hard cheese samples. The results of this study indicate that presence of nitrates and nitrites above the desirable limit in milk and milk products act as heath hazard for man consuming such contaminated products

Aditivos de las presentaciones medicamentosas / Additive of the medical samples

La Tartrazina y Sulfitos son responsables del 90%de las reacciones a los aditivos. Colorantes como Amaranto (Rojo Nro.4), Eritrocina (Rojo Nro.3), Azul Brillante (Azul Nro.1), etc. y conservantes como parabenos, nitratos, benzoatos, etc., son citados por reportes aislados en la literatura como causantes de racciones medicamentosas. En nuestro país la mayoría de prospectos de los medicamentos no detallan los excipientes. Se inició el presente trabajo revisando uno por uno los prospectos adjuntos de las presentaciones farmacéuticas, en farmacias y droguerías de nuestra ciudad. Se agruparon los medicamentos en 5 categorías. Se enviaron cartas a 104 de los Laboratorios, solicitando nos confirmen o nos rectifiquen, si existe error en cuanto a la lista de presentaciones farmacéuticas que adjuntamos. Así tenemos: 1)Medicamentos con sulfitos. Ej: Biletan (comp.), Gentamina (amp.). 2)Medicamentos con tartrazina. Ej: Pankreoflat AD (comp.). 3)Medicamentos que no aclaran excipientes. Ej.: Berco (susp.) 4)Medicamentos que aclaran excipientes, sin sulfitos, ni tartrazina. Ej.: Ventolin (cpto)(jarabe). 5)Medicamentos que no se conocen sus prospectos por falta de existencia. Ej.:Amplidine Balsámico (susp.). Hay laboratorios que colaboran y otros que no contestaron nuestras cartas. El listado de las presentaciones medicamentosas, resultante de este trabajo, permitirá que los médicos alergólogos, tomen conocimiento de los excipientes que en ciertos pacientes sensibles pueden causar reacciones

Nitratos e nitritos: presença em alimentos e riscos de sua ingestäo / Nitrates and nitrites: presence in foods and risks of intake

O artigo aborda a ocorrencia natural de nitratos e nitritos em alimentos e seu uso intencional como conservadores em produtos cárneos curados. Säo discutidos efeitos adversos à saúde atribuídos à ingestäo de nitratos e nitritos, incluindo induçäo de metemoglobinemia e formaçäo de N-nitrosaminas. Säo também apresentados dados sobre os níveis de nitratos, nitritos e N-nitrosaminas em alguns alimentos

Nitratos, nitritos e compostos N-nitrosos em alimentos: onde está o problema? / Nitrates, nitrites and N-nitrosocompounds in foods: where is the problem?

O objetivo deste artigo de revisäo é apresentar os problemas associados à presença de nitratos, nitritos e compostos. N-nitrosos em alimentos. Säo fornecidas informaçöes sobre as propriedades físico-químicas dos compostos, sua presença natural em vegetais e em alimentos processados, bem como os efeitos produzidos na exposiçäo humana: aspectos toxicológicos relacionados à ingestäo de nitratos e nitritos por adultos e crianças e á carcinogenicidade dos compostos N-nitrosos