Environmental Project, 944 – Evaluation of Health Hazards by exposure to Triazines and Degradation Products

Evaluation of Health Hazards by exposure to Triazines and Degradation Products

6 Summary and evaluation

6.1 Description

Atrazine, simazine, terbutylazine and cyanazine are triazines, which have been used or still are in use in agriculture as herbicides in Denmark. Desethyl atrazine (DEA), desisopropyl atrazine (DIA), desethyl terbutylazine, desethyldesisopropyl atrazine (DACT), hydroxyatrazine, hydroxysimazine, and hydroxyterbutylazine are some of the degradation products of these triazines.

The triazines are colourless to white powders with low water solubilities (5-170 mg/l) and vapour pressures lower than 10^-6 mmHg.

6.2 Environment

There are no known natural sources of atrazine. Virtually the entire production volume is released to the environment, primarily soils, mainly as a result of agricultural and other weed-control practices.

In the atmosphere, atrazine will exist in both the particulate and vapour phases. Particulate phase atrazine will be removed from the atmosphere by wet and dry deposition. Vapour phase atrazine can be degraded in the atmosphere by reaction with photochemically produced hydroxyl radicals; a half-life of 14 hours has been estimated.

The triazines may be transported from where they are applied to soils by runoff into surface water and percolation into groundwater. Atrazine, simazine and terbutylazine tend to persist in surface and groundwater (no or slow abiotic hydrolysis and photolysis, and degradation half-lives of 26-253 days), with a moderate tendency to bind to sediments (dissipation half-lives for the water phase of 6-134 days in controlled aerobic water-sediment systems). When atrazine is degraded in aquatic systems, hydroxytriazine, desethyl atrazine (DEA) and desisopropyl atrazine (DIA) are the major products formed.

Field studies in Europe showed average half-lives in soil of 29, 64-130, and 22 days for atrazine, simazine, and terbutylazine, respectively. For simazine, the half-life was shown to be higher following application at fall (130 days) than following application at spring (64 days). High microbial activity enhanced the degradation.

Regarding ground water contamination, the most important metabolites from atrazine, simazine, and terbutylazine were desethyl atrazine (DEA), desisopropyl atrazine (DIA), and hydroxyatrazine; desisopropyl atrazine (DIA); and hydroxyterbutylazine, and desethyl terbutylazine, respectively.

Atrazine has a slight to moderate tendency to bioconcentrate in microorganisms, algae, aquatic invertebrates, worms, snails, or fish.

6.3 Human exposure

Occupational exposure to triazines may occur through dermal contact or inhalation during the manufacture, formulation or application of the herbicides. The general population may be exposed to the triazines and their degradation products through their widespread occurrence in the environment especially in drinking water. No significant exposure is expected to occur via foodstuffs.

6.4 Toxicokinetics

In general, triazines are well absorbed in rats by the oral route (50-70%). Following dermal exposure in humans only about 5% of the dose is absorbed. No data were found on the toxicokinetics following inhalation. The triazines are extensively metabolised and eliminated with a half-life of 10-20 hours via urine but also in faeces.

The main biotransformation pathways for the triazines in rats are N-dealkylation by the hepatic cytochrome P450 system, and glutathione conjugation of either the parent compound or the N-dealkylated metabolite to the ultimately excreted mercapturic acid conjugate. Rats and humans produce the same type of metabolites following exposure to atrazine, but species-specific differences in the metabolite ratios are found.

Desethyldesisopropyl atrazine (DACT) is a major metabolite of atrazine and simazine. Desisopropyl atrazine (DIA) is also a metabolite of atrazine and simazine. Desethyl atrazine (DEA) is a metabolite of atrazine, desethyl terbutylazine is a metabolite of terbutylazine, and desethyl cyanazine is a metabolite of cyanazine.

6.5 Mode of action

Because of a common mode of action, US-EPA has grouped atrazine, simazine and their degradation products desethyl atrazine (DEA), desisopropyl atrazine (DIA), and desethyldesisopropyl atrazine (DACT). Hydroxyatrazine was not included in this group based on the absence of mammary gland tumour induction and inconclusive data on its effect on the luteinizing hormone.

Treatment of laboratory animals with the triazines results in toxic effects such as mammary gland tumours in female Sprague-Dawley rats and reproductive and developmental alterations. The primary proposed mode of action for these tumours and some of the reproductive and developmental effects involves disruption of the hypothalamic-pituitary-gonadal axis resulting in a decreased serum level of luteinizing hormone, and as a consequence an increased serum level of oestrogen and prolactin.

IARC and US-EPA have concluded that the mechanism by which atrazine increases the incidence of mammary gland tumours in Sprague-Dawley rats is not relevant to humans.

6.6 Human toxicity

6.6.1 Single and repeated dose toxicity

No data were found.

6.6.2 Skin irritation

Case-reports exist of contact dermatitis in workers exposed dermally to atrazine, simazine and/or cyanazine.

6.6.3 Sensitisation

An 0.5% suspension of a formulation of atrazine or simazine did not cause skin sensitisation on repeated application to humans.

6.6.4 Toxicity to reproduction

The use of atrazine was not associated with any decrease in fecundity, increased odds ratios for miscarriage, pre-term delivery, or babies who were small for gestational age in two surveys of Canadian couples on farms.

An ecological study in USA found a greater risk of intrauterine growth retardation in live births by women in 13 communities served by a water system containing elevated levels of triazines. No definite causal relationship could be determined.

6.6.5 Mutagenic and genotoxic effects

No statistically significant increase in micronucleus formation and sister chromatid exchange of peripheral blood lymphocytes was found in 34 males exposed to simazine in the drinking water at levels of 10 to 30 ppm.

6.6.6 Carcinogenic effects

In cohort studies of agricultural chemical workers, an increase in the number of deaths from non-Hodgkin lymphoma was observed. In one of the studies, the increase was significant but the 4 observed cases were not concentrated in the subgroup with long duration of employment and many years since hire. In a companion study of cancer incidence in the same group of workers, a 1.8-fold increase in prostate cancer incidence was found. Bias could not be ruled out as a reason for this increase.

Case-control studies have shown an association between non-Hodgkin lymphoma and use of atrazine. When the odds ratios were adjusted for use of other pesticides, the association was not significant. Recently, a study has shown a small but statistically significant association between atrazine exposure and the non-Hodgkin lymphoma subtype defined by t(14;18) chromosomal translocation.

In a nested case-control study in USA within a cohort of a predominantly Hispanic labour union, an elevated risk of prostate cancer was found in farm workers with relative high exposure to simazine compared to workers with lower levels of exposure.

In a case-control study in Italy, the odds ratios for primary malignant epithelial tumours of the ovary were significantly increased for definitely exposed and non-significantly increased for possibly exposed. The odds ratios were not adjusted for exposure to other types of pesticides.

Case-control studies of Hodgkin's lymphoma, soft-tissue sarcoma, colon cancer, leukaemia, and multiple myeloma showed no significant excess risk among persons handling triazine herbicides.

Ecological studies in which no individual exposure data are available have found a correlation between atrazine use/levels and certain cancers (brain, stomach, testis, and prostate cancers, and leukaemia. For other cancers (non-Hodgkin's lymphoma, soft-tissue sarcoma, ovarian, breast, and colon cancer) no or inverse associations have been found.

IARC have concluded that there is inadequate evidence in humans for the carcinogenicity of atrazine and simazine.

6.7 Animal toxicity

6.7.1 Single dose toxicity

Single inhalatory, peroral or dermal administration of the triazines in general proved to be only slightly toxic (LC50-values for rats are greater than 5300 mg/m³ for atrazine, simazine, and terbutylazine; oral LD₅₀-values for rats, mice, rabbits, and hamsters ranged from 670 to 7700 mg/kg for atrazine, simazine and terbutylazine; and dermal LD₅₀-values for rats and rabbits are greater than 2000 mg/kg for atrazine, simazine, and terbutylazine). However, for cyanazine the oral LD₅₀-values were lower than for the other triazines (ranged from 140 to 840 mg/kg for rats, mice, and rabbits).

For the degradation products, oral LD₅₀-values for rats were greater than 2360 mg/kg for desethyldesisopropyl atrazine (DACT), hydroxyatrazine, and hydroxysimazine. For desethyl atrazine (DEA) and desisopropyl atrazine (DIA), oral LD₅₀-values for rats were lower for females (670-810 mg/kg) than for males (1890-2290 mg/kg).

6.7.2 Irritation

The triazines were none to moderately irritating to the rabbit skin and eye.

6.7.3 Sensitisation

Atrazine is classified for skin sensitisation based on positive results in the guinea pig maximization test and optimisation test . Simazine, terbutylazine and cyanazine did not cause appreciable skin sensitisation in the guinea pig.

6.7.4 Repeated dose toxicity

No data were found on repeated dose toxicity with inhalation of triazines.

Most studies on repeated dose toxicity following oral exposure have been performed with atrazine but studies also exist for simazine, terbutylazine, cyanazine, desethyl atrazine (DEA), desisopropyl atrazine (DIA), desethyldesisopropyl atrazine (DACT), and hydroxyatrazine. See Table 10 and Table 12 for the lowest NOAELs/LOAELs for the repeated dose toxicity effects (following oral exposure) mentioned in this chapter.

In general, the triazines and their degradation products decreased body weight and/or food consumption.

Several studies mainly in Sprague-Dawley rats focused on the ability of the triazines (especially atrazine) to cause neuroendocrine effects. It was shown that they attenuated the luteinizing hormone surge, disrupted the oestrous cycle, increased the serum level of oestrogen and prolactin, increased the relative pituitary weights, decreased the testes and prostate weights, and "thickened" mammary glands at doses from 3.7 mg/kg bw/day and with a NOAEL of 1.8 mg/kg bw/day in rats and with a LOAEL of 1 mg/kg bw/day in pigs.

In addition to the neuroendocrine effects, haematological changes were observed (anaemia, increased myeloid hyperplasia in the bone marrow, extramedullary haematopoiesis in the liver and spleen and haemosiderin pigment in the spleen) in several species. In 2-year studies, the Sprague-Dawley rat seems to be more sensitive to the hormonal as well as the haematological changes than the Fischer 344 rat in which these effects were absent at the doses tested. The haematological changes seem to be most severe in the rats dosed with cyanazine, atrazine, and desisopropyl atrazine (DIA) based on their ability to induce extramedullary haematopoiesis. With these three chemicals, the haematological changes also seem to be more severe in the rats than in the other species tested. In the rats dosed with the other triazines or degradation products, anaemia was the only sign of haematological toxicity. Cyanazine had the lowest LOAEL of 2.1 mg/kg bw/day and a NOAEL of 0.99 mg/kg bw/day for haematological changes.

Generally at the same or higher doses than the haematological changes, kidney toxicity was detected in some of the studies in several species in the form of changes in mainly weight and/or histopathology of the kidney. The kidney toxicity seems to be most severe for hydroxyatrazine where a dose of 17 mg/kg bw/day to rats caused excessive mortality predominantly caused by renal failure. At the lower dose of 7.8 mg/kg bw/day, severe kidney toxicity was also observed while the NOAEL was 0.96 mg/kg bw/day.

Cardiac toxicity was detected in dogs, pigs and rabbits but not in rats. In the dog, the cardiac toxicity was quite severe with clinical signs, ECG alterations, heart weight changes, and/or macroscopic and histopathological findings at doses from about 24 mg/kg bw/day and with a NOAEL of 3.4 mg/kg bw/day. For hydroxyatrazine, no cardiac toxicity was observed in the dog at doses up to 200 mg/kg bw/day. In the only study with pigs dosed with atrazine, the LOAEL (2 mg/kg bw/day) and the NOAEL (<2 mg/kg bw/day) were lower than in the dog studies.

Only four studies (one with atrazine, one with simazine, and two with terbutylazine) were found on repeated dose toxicity following dermal exposure. All three studies were performed in rabbits and showed decreased body weight gain and food consumption. Haematological changes were observed in the study with atrazine but at much higher doses than in the studies with oral exposure. The exposed rabbits had slight to moderate irritation of the skin.

6.7.5 Toxicity to reproduction

No developmental toxicity was seen in rats exposed by inhalation to concentrations up to 317 mg/m³ of simazine on days 7-14 of gestation.

Two studies have been performed with mixed oral exposure to the triazines.

In the first study, groups of pregnant rats were gavaged on gestational day 15-19 with 0, 0.044, 0.087, 0.44, 0.87, 4.4, and 8.7 mg/kg bw/day of a mixture of atrazine (25%), desethyl atrazine (DEA)(15%), desisopropyl atrazine (DIA) (5%), desethyldesisopropyl atrazine (DACT) (35%), and hydroxyatrazine (20%).

Only the male offspring were studied. It was unclear from the study abstracts if preputial separation (a marker of male puberty in the rat) was statistically significantly delayed. At some of the doses the male offspring had significantly larger anterior pituitary gland weights and the ventral prostate weight was significantly smaller while the lateral prostate, testes, and seminal vesicle weights were unaffected by treatment. At some of the doses the male offspring exhibited an increase in the concentration of serum testosterone and oestrone while the concentrations of serum and pituitary prolactin, serum oestradiol, and thyroid stimulating hormone were unaffected by treatment. A dose-dependent increase in the incidence of lipomatous masses nested in epididymal fat pads was noted. Lateral prostate inflammation was observed in several of the dose groups. However, the incidence and severity remained to be quantified via histopathology and immunohistochemistry. Based on the limited data from the study abstracts, it is impossible to set a NOAEL.

In the second study, atrazine, simazine, and cyanazine were administered at individual maximal concentrations of about 30-50 g/l (equivalent to about 0.0075-0.013 mg/kg bw/day) of drinking water in a mixture containing several other pesticides, fertilizers and other organic substances commonly found in groundwater in California, USA. No effects on several reproductive parameters in mice and on developmental toxicity in rats were observed.

Most studies on toxicity to reproduction following oral exposure to individual triazines and their degradation products have been performed with atrazine but studies also exist for simazine, terbutylazine, cyanazine, desethyl atrazine (DEA), desisopropyl atrazine (DIA), desethyldesisopropyl atrazine (DACT), and hydroxyatrazine. Reproductive as well as pre- and postnatal developmental studies have been performed mainly in rats but for a few of the prenatal studies also in rabbits. See Table 10 and Table 11 for the lowest NOAELs/LOAELs for the reproductive and developmental effects (following oral exposure) mentioned in this chapter.

In general, the triazines and their degradation products decreased body weight gain in parental animals and sometimes in pups. In the prenatal studies, they were not developmental toxicants when administered in doses that were not maternally toxic (mainly decreased body weight gain).

For all of the studied triazines and degradation products, an increased incidence of incomplete ossification sites in foetuses and/or fused sternebrae was observed with about equal sensitivity in rats and rabbits. Cyanazine seems to be more potent than the other triazines and degradation products in inducing this effect with a LOAEL of 5 mg/kg bw/day and 2 mg/kg bw/day for rats and rabbits, respectively, and a NOAEL of < 5 mg/kg bw/day and 1 mg/kg bw/day for rats and rabbits, respectively. However, the lower NOAEL/LOAEL for rats could possibly be due to the use of the Fischer 344 rat, which in the cyanazine studies seem to be more sensitive to this effect than the Sprague-Dawley rat.

Cyanazine but not any of the other triazines or degradation products induced microphtalmia/anophtalmia, diaphragmatic hernia associated with liver protrusion, and dilated brain ventricles in foetuses of rats and rabbits although at a higher dose than required for induction of incomplete ossification sites.

Mild neurobehavioral effects were observed in rat pups of dams, which had been dosed with atrazine a month before mating. This effect was not studied for the other triazines and degradation products.

Several studies focused on the ability of the triazines and their degradation products to cause neuroendocrine effects. It was shown in prenatal studies in rats and rabbits that they might cause altered pregnancy outcome (pre- and postimplantation loss, full litter resorption, delayed parturition) with NOAELs of 17-40 mg/kg bw/day and LOAELs of 34-91 mg/kg bw/day for Fischer 344 rats. From the studies with cyanazine it seems that the NOAELs/LOAELs for the altered pregnancy outcome may be lower for rabbits than for rats. For atrazine, the preimplantation loss was observed in Fischer 344 rats while the postimplantation loss was observed in Holtzman rats, Charles River CD rats, and rabbits. The Fischer 344 rats were more sensitive than the Sprague-Dawley and Long-Evans rats to full litter resorption in dams dosed on gestation days 6-10. No full litter resorption occurred when the rats were dosed on gestation days 11-15 suggesting that the full litter resorption is maternally mediated and consistent with loss of luteinizing hormone support of the corpora lutea. Holtzman, Sprague-Dawley, Long-Evans, and Fischer 344 dams participating in the prenatal studies all had a decreased serum level of luteinizing hormone. However, only Sprague-Dawley dams had an increased serum level of oestrogen.

It was shown in postnatal studies mainly in Wistar rats that the triazines and their degradation products decreased the serum testosterone level, and the prostate, testes, seminal vesicle, epididymal, and/or anterior pituitary weights. An in vitro experiment demonstrated that atrazine directly inhibited Leydig cell testosterone production. Generally at lower doses than the doses causing the effects on the serum testosterone level and on the weights of the male reproductive organs, the triazines and their degradation products delayed the preputial separation of male rats and delayed the vaginal opening of female rats dosed postnatally indicating a delayed puberty of the rats. These studies were mainly performed with Wistar rats. A study with atrazine indicated that the Sprague-Dawley rat was more sensitive to delayed vaginal opening than the Wistar rat. Male rats seem to be more sensitive than female rats to the delayed puberty. For male rats, DACT had the lowest NOAEL/LOAEL of 4.4/8.4 mg/kg bw/day. Atrazine at 13 mg/kg bw/day suppressed suckling-induced prolactin release in Wistar rat dams at postnatal days 1-4 and 6-9. The NOAEL was 6.3 mg/kg bw/day. This suppression resulted in an increased incidence and severity of prostate inflammation in the male offspring. This effect was not studied for any of the other triazines or degradation products.

No data were found on toxicity to reproduction with dermal contact with triazines.

Atrazine administered intraperitoneally to male rats affected the spermatogenesis. Histological changes of the rat testis and degenerative changes in Leydig and Sertoli cells were observed.

6.7.6 Mutagenic and genotoxic effects

Overall, the triazines and their degradation products tested negative for mutagenic and genotoxic effects in bacteria and mammalian cells (in vitro and in vivo), although a few positive results did occur.

6.7.7 Carcinogenic effects

No data were found on carcinogenic effects following inhalation of or dermal contact with triazines.

Most studies on carcinogenicity following oral exposure have been performed with atrazine but a few studies exist for simazine, terbutylazine, cyanazine, desethyldesisopropyl atrazine (DACT), and hydroxyatrazine.

In general, the triazines and their degradation products seem to increase the incidence and cause an earlier onset of mammary gland tumours (fibroadenomas, adenocarcinomas) only in intact female Sprague-Dawley rats (and not in Fischer 344 rats, CD-1 mice or ovariectomised Sprague-Dawley rats). However, hydroxyatrazine was not carcinogenic in the carcinogenicity study with Sprague-Dawley rats. The lowest doses at which the triazines increased the incidence and/or caused an earlier onset of mammary gland tumours were 1.5, 5.3, 53, 1.4, and 10 mg/kg bw/day for atrazine, simazine, terbutylazine, cyanazine, and DACT, respectively. The NOAELs for carcinogenicity in Sprague-Dawley rats were 0.5, 0.52, 7.0, 0.26, and 3.5 mg/kg bw/day, respectively.

An increased incidence of Leydig cell tumours was observed in one study with atrazine and in one with terbutylazine in Sprague-Dawley rats at doses of about 50 mg/kg bw/day. In one of the studies, the incidence fell within historical control data and was attributed in part to the better survival of these animals, and in the other study, the tumours were observed mainly in the old rats.

An increased incidence of pituitary gland carcinomas was observed in one study with simazine in female Sprague-Dawley rats at doses of about 46 mg/kg bw/day. The incidence fell within historical control data. In the same study, a small increase in renal tubular tumours was observed in both sexes at the same dose based on which the European Commission has classified simazine for carcinogenicity.

IARC have concluded that there is sufficient evidence in experimental animals for the carcinogenicity of atrazine and that there is limited evidence in experimental animals for the carcinogenicity of simazine.

However, IARC and US-EPA have concluded that there is strong evidence that the mechanism by which atrazine increases the incidence of mammary gland tumours in Sprague-Dawley rats is not relevant to humans.

6.8 Evaluation

6.8.1 Critical effect(s) and NOAEL(s)

The overall critical effect in humans following exposure to triazines and their degradation products are considered to be the neuroendocrine effects (hormonal disturbances and reproductive and developmental effects caused by the disruption of the hypothalamic-pituitary-gonadal axis). This is based on the following:

In humans, the available data on health effects are mainly focused on the possible carcinogenic effects. The usefulness of many of these studies are limited because mixed exposure often has occurred. IARC has concluded that there is inadequate evidence in humans for the carcinogenicity of atrazine and simazine. A few studies have focused on toxicity to reproduction without significant findings.

In laboratory animals, the main effects observed is the neuroendocrine effects, haematological changes, cardiac toxicity, kidney toxicity, incomplete ossification sites and/or fused sternebrae in foetuses, and microphtalmia/anophtalmia, diaphragmatic hernia associated with liver protrusion, and dilated brain ventricles in foetuses. Overall, the hormonal disturbances occur at lower doses than the other effects.

However, for hydroxyatrazine the critical effect seem to be kidney toxicity which occur at lower doses than the neuroendocrine effects and seem to be more severe than for the other triazines and degradation products for which data exist. In addition, hydroxyatrazine causes delayed puberty and altered pregnancy outcome (pre- and postimplantation loss, full litter resorption and delayed parturition) but mammary tumours in Sprague-Dawley rats does not occur suggesting that the main mode of action for hydroxyatrazine might be different from the other triazines and degradation products. However, since the NOAEL for kidney toxicity of hydroxyatrazine is higher than some of the NOAELs seen for the neuroendocrine effects in the other triazines and degradation products, setting an overall NOAEL for neuroendocrine effects will also cover the kidney toxicity caused by hydroxyatrazine.

For cyanazine, decreased kidney function has been observed in one poorly reported 4 week rat study from 1968 at very low doses, but in a newer 2-year rat study from 1990, no kidney toxicity was observed at doses that were higher than the doses causing neuroendocrine effects. As the only triazine, cyanazine is causing microphtalmia/anophtalmia, diaphragmatic hernia associated with liver protrusion, and dilated brain ventricles in foetuses suggesting that cyanazine might have an additional mode of action compared to the other triazines and degradation products. However, cyanazine is also causing neuroendocrine effects (mammary gland tumours and altered pregnancy outcome) and at lower doses than the doses causing the developmental effects. Therefore, for cyanazine the critical effect is considered to be the neuroendocrine effects.

The European Commission has classified simazine for carcinogenicity based on a small increase in renal tubular tumours at the highest dose tested in one rat study. Since simazine is not mutagenic and genotoxic and the renal tumours occur only in small numbers at a relatively high dose it is likely that a threshold exist for these tumours although the mechanism is unknown. Simazine is causing neuroendocrine effects at lower doses than the doses causing renal tumours. Therefore, for simazine the critical effect is considered to be the neuroendocrine effects.

The neuroendocrine effects are mainly ascribed to a disruption of the hypothalamic-pituitary-gonadal axis resulting in a decreased serum level of luteinizing hormone, and an increased serum level of oestrogen and prolactin. In one prenatal study with atrazine, it was shown that atrazine was able to decrease the serum level of luteinizing hormone in several strains of rats but in the same study it was only the Sprague-Dawley rat that had an increased level of serum oestrogen suggesting that all rat strains are sensitive to triazine-induced hormonal disturbances but the Sprague-Dawley rat is more sensitive than the other rat strains to the effect on the serum oestrogen level. This will also explain why the mammary gland tumours (proposed to occur because of a constant elevated serum level of prolactin and oestrogen) were observed only in studies with Sprague-Dawley rats. IARC and US-EPA have concluded that there is strong evidence that the mechanism by which atrazine increases the incidence of mammary gland tumours in Sprague-Dawley rats is not relevant to humans. The mammary gland tumours are generally seen at lower doses than the other endocrine effects. Nevertheless in keeping to the proposed mode of action, the serum level of luteinizing hormone is expected to be decreased at the doses causing tumours. US-EPA has concluded that it is not unreasonable to expect that atrazine might cause adverse effects on hypothalamic-pituitary function in humans and that the same endocrine perturbations that induce tumours also appear to play a role in at least some reproductive developmental effects which may be relevant to humans. For rats it has e.g. been suggested that the full litter resorption is maternally mediated and consistent with loss of luteinizing hormone support of the corpora lutea. A decreased serum level of luteinizing hormone will most likely also influence the human reproduction and development. Therefore in selecting an overall NOAEL for the human risk characterisation of the triazines and their degradation products in drinking water it seems reasonable to select a NOAEL from the carcinogenicity studies. In general, cyanazine seems to be more toxic than the other triazines and their degradation product. This is also the case for the combined chronic toxicity/carcinogenicity study with cyanazine where a NOAEL of 0.20 mg/kg bw/day was established based on mammary tumours in female rats, decreased body weight gain in both sexes of rats, and increased hyperactivity in the male rats at the next dose level.

Two reproductive and/or developmental studies have been performed with mixed exposure to the triazines. In the first study, where pregnant rats were exposed to a mixture of atrazine and its degradation products, neuroendocrine developmental effects might have occurred in the male offspring at doses lower than 0.20 mg/kg bw/day but based on the limited data from the study abstracts, it is impossible to set a NOAEL. In the second study, no effects on several reproductive parameters in mice and on developmental toxicity in rats were observed when atrazine, simazine, and cyanazine were administered at individual concentrations of maximal 0.013 mg/kg bw/day (the highest individual dose tested) in a mixture containing several other pesticides, fertilizers and other organic substances.

The NOAEL of 0.20 mg/kg bw/day will be used as the overall NOAEL for the human risk characterisation of the triazines and their degradation products in drinking water.