Fate of the herbicide 14C-terbuthylazine in Brazilian soils under various climatic conditions.

14C-terbuthylazine was applied to three Brazilian soils in closed aerated laboratory microcosms, both under standardized and under natural Brazilian climate conditions. Volatilization from soil to air, leaching from soil to percolate water, and transport from upper to deeper soil layers were higher in sandy soil than in clay soil and in organic soil. Mineralization of 14C-terbuthylazine to 14CO2 was higher in sandy soil than in clay and organic soils under standardized climatic conditions, whereas it was higher in organic soil than in sandy soil under Brazilian summer conditions. Under natural Brazilian summer conditions, leaching as well as vertical transport within the soil were enhanced as compared to standardized climate conditions comprising lower precipitation rates; volatilization was strongly reduced under high irrigation conditions.

Formation and release of residues of the 14C-labelled herbicide isoproturon and its metabolites bound in model polymers and in soil.

The humic monomer catechol was reacted with (14)C-isoproturon and some of its metabolites, including (14)C-4-isopropylaniline, in aqueous solution under a stream of oxygen. Only in the case of (14)C-4-isopropylaniline, incorporation in oligomers, in fulvic acid-like polymers, and in humic acid-like polymers by covalent bonds was observed. The main oligomer was identified by mass spectrometry as a trimer, 4,5-bis-(4-isopropylphenylamino)-3,5-cyclohexadiene-1,2-dione. Biomineralization of (14)C-compounds to (14)CO(2) in a loamy soil and release of (14)C from soil columns into percolate water decreased in the order: free isoproturon >free 4-isopropylaniline>fulvic acid-like polymers>trimer>humic acid-like polymers. In soil columns, a small but measurable migration of (14)C from polymers from upper to deeper soil layers could be detected; most of this (14)C was bound again in a non-extractable form. It is concluded that aniline-derived pesticides bound in soil by covalent binding may not be fully undegradable, nor fully immobile.

Mobility of the organochlorine compound dicofol in soil promoted by Pseudomonas fluorescens.

The genetic modified Pseudomonas fluorescens Br 12, resistant to kanamycin and rifampycin, was used to follow the cotransport of the organochlorine acaricide dicofol through a nonsterilized soil column. P. fluorescens was found to bioaccumulate dicofol with the highest bioconcentration factor of 279 within 30 min. Separate soil column experiments where applied P. fluorescens or [14C]dicofol were submitted to heavy rain simulation did not reveal any correlation between the distribution patterns of P. fluorescens and [14C]dicofol in the leachate fractions (r = 0.3). Similar experiments with P. fluorescens that previously had bioaccumulated [14C]dicofol demonstrated a high correlation of these bacteria and radioactivity in the leachate fractions (r = 0.8). The total recovery of radioactivity in the leachate, when [14C]dicofol was previously bioaccumulated in bacteria, was more than two times higher (4.5%) than the total recovery of radioactivity in the leachate when [14C] dicofol was directly applied in the soil (2%). This indicates cotransport by Pseudomonas. Fractionation and analysis of soil columns indicated that most of the bioaccumulated dicofol was rapidly released and adsorbed in soil, while bacteria moved down by leaching.

A model for the formation and degradation of bound residues of the herbicide 14C-isoproturon in soil.

The humic monomer catechol was reacted with 14C-isoproturon and some of its metabolites, including 14C-4-isopropylaniline, in aqueous solution under a stream of oxygen. Only in the case of 14C-4-isopropylaniline, incorporation in oligomers, in fulvic acid-like polymers, and in humic acid-like polymers was observed. The main oligomer was identified by mass spectrometry as 4,5-bis-(4-isopropylphenylamino)-3,5-cyclohexadiene-1,2-dione. Oligomers and polymers containing bound 14C-4-isopropylaniline were subjected to biodegradation studies in a loamy agricultural soil during 55 days by quantifying 14CO2 evolved. In all cases, significant mineralization rates could be determined, which, however, were much smaller than those of free 14C-4-isoproturon and free 14C-4-isopropylaniline in the same soil.

Predicting bioconcentration factors (BCFs) of polychlorinated bornane (Toxaphene) congeners in fish and comparison with bioaccumulation factors (BAFs) in biota from the aquatic environment.

Polychlorinated bornanes, the main components of Toxaphene, are bioconcentrated in aquatic organisms to a high extent. However, up to this time no bioconcentration tests with individual chlorinated bornanes in aquatic organisms have been performed. Therefore, the bioconcentration factors (BCFs) of seven selected persistent chlorinated bornane congeners which are regularly found in aquatic organisms, were predicted from their n-octanol/water partition coefficients (log Kow). Furthermore, these BCF values were compared with the measured bioaccumulation factors (BAFs) in zooplankton and different fish species from the aquatic environment.

Formation, characterization and release of non-extractable residues of [14C]-labeled organic xenobiotics in soils.

The amount of non-extractable residues (NER) of organic xenobiotics in the soil can considerably exceed the amount of extractable residues which are accessible to normal residue analysis. The NER therefore present a burden to the soil, the toxicological and ecotoxicological potential of which is largely unknown. For the characterization of bound residues and their binding type, special solubilization methods such as supercritical fluid extraction are applied and experiments with radiolabeled model polymers are performed. Mineralization experiments with [(14)C] labeled xenobiotics in natural soil show that a total degradation is still also possible in the environment when in a bound form. Ecotoxicological effects of non-extractable residues may be recorded when their concentration is high, when the parent compound exhibits a high ecotoxicity and the applied detection method is sufficiently sensitive.

S-triazine residues in groundwater.

In the last years, the occurrence of pesticides and other chemicals in groundwater has been confirmed. The herbicide atrazine is among the pesticides most frequently detected in groundwater. In groundwater samples from the United States atrazine concentrations reached levels up to 10 micrograms/1. In our lysimeter experiments with radioactive labelled terbuthylazine we measured 2.87-4.20% of the applied radioactivity after 1160 days in the leachate.

Considerations on genetic and environmental factors that contribute to resistance or sensitivity of mammals including humans to toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. Part 1: Genetic factors affecting the toxicity of TCDD.

The marked species differences in short-term toxicity (30-day LD50) of ca. 10,000 (LD50: guinea pigs ca. 1 microgram/kg body wt and Han/Wistar Kuopio rats more than 9600 micrograms/kg body wt) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is one of the central issues of the controversies that have developed on the validity of risk assessment strategies for TCDD and related compounds. One of the most challenging issues that toxicologists face today is the identification of genes that contribute to or are responsible for increased resistance or sensitivity to TCDD and related compounds. It is assumed that most, if not all, toxic effects of TCDD are mediated more or less through the binding affinity to the Ah receptor. This hypothesis was extended and tries to explain the differences in sensitivity/resistance of animals including humans to TCDD by their total fat (lipid) content. In this respect the gene or genes which is or are responsible for obesity of mammals including humans are of great interest. An obvious linear positive logarithmic relationship between the oral 30-day LD50 (microgram/kg) of TCDD in different species and strains of mammals and their total body fat content (TBF%) was found: log LD50 = 5.30 x log (TBF)-3.22, or LD50 = 0.000603 x (TBF)5.30. By means of this regression the toxicity of TCDD in mammals including humans of different age and/or body weight can be predicted if their total body fat content is known. Examples of single-gene and polygenic disease models in different mammals, such as nonobese diabetic, diabetic, viable yellow, obese, and fat mice, as well as transgenic mice, and other suitable animal models, such as fatty Zucker rats, Han/Wistar (Kuopio) rats, and minipigs, are discussed, and predicted LD50 values of TCDD in these animals and humans are presented.

Mineralization kinetics of chemicals in soils in relation to environmental conditions.

The mineralization kinetics of the detergent n-dodecylbenzenesulfonate ([14C]LAS) and the plasticizer di(2-ethylhexyl)phthalate ([14C]DEHP) were studied in three fresh sampled soils of different type. Time series of 14CO2 evolution were fitted with various linear and nonlinear models. The kinetics could be represented best by a 3/2-order function with linear adaptation and three parameters: x1 describing the gradient of the exponential part of the curve, x2 the lag phase, and x3 the last, asymptotic part. These parameters as well as the maximal degraded amounts (A) were correlated with various environmental conditions. For LAS, A was similar in all three soils and was positively related to pH in two soils and to humidity in one soil (rendzina). The parameters x1-x3 were positively influenced by soil humidity in all three soils. The degraded amounts A, expressed as percentage of added dose, were independent of initial concentration. Both A and the parameters x1-x3 increased with increasing temperature. Degradation was negligible below 3 degrees C. For DEHP, the degradation was much slower than that of LAS and was most rapid and most complete in the rendzina soil. Relative degradation A was lower for higher initial application rates. Temperature influenced both A and the lag phase. Degradation was not significant below 10 degrees C.

The relevance of aquatic organisms' lipid content to the toxicity of lipophilic chemicals: toxicity of lindane to different fish species.

The acute toxicity (48-hr LC50) of lindane (gamma-HCH) to 16 fish species, belonging to eight families, ranges from 22 to 900 micrograms/liter (mean: 150 micrograms/liter). A significant positive linear relationship between the lipid content (% on a wet weight basis) of the fishes and their toxicity to gamma-HCH was found. If the toxicity is referred to 1% lipid, 48-hr LC50 values range between 13.2 and 32 micrograms/liter, and thus the coefficient of variation of the mean is reduced from 139 to 22%. It is concluded that the lipids of aquatic organisms serve as a protective reservoir against the toxic effects of lindane and other lipophilic, relatively persistent organic chemicals, because they are bioconcentrated mainly in the body lipids. Therefore, in organisms with high lipid content, only a relatively small fraction of the hydrophobic chemical can reach target organs (nerves, liver, etc.) and/or receptors. For comparing toxicity data of organic chemicals to aquatic organisms, the total lipid content of the organisms must be considered. The results of this investigation are important in comparative environmental toxicology for risk assessment of freshwater and marine organisms.

Uptake pathways of chlorobenzenes in plants and their correlation with N-octanol/water partition coefficients.

The bioconcentration factors of 14C-labeled chlorinated benzenes in plants from soil were quantified in short-term laboratory experiments and correlated to Kow. The correlation was negative for barley and positive for cress. In order to interpret these opposite results, the log/log correlation between partition coefficients and Kow of the chemicals was established also for each step of the uptake, via both roots and leaves. For the first step of root uptake--the partition of the chemicals from soil solids into soil water--the correlation with Kow was negative, whereas it was positive for the second step, the partition roots/soil water, of both plant species. Similarly, the correlation between the first step of foliar uptake--the partition of the chemical from soil into air--and Kow was negative, and that between the second step--the partition between aerial plant parts and air--and Kow was positive for both plant species. The slopes of the regression lines differed between plant species. It may be concluded that Kow can be used as a parameter to predict the uptake of chemicals from soil by plants only if the same class of chemicals and the same plant species is considered.

Bioconcentration of superlipophilic persistent chemicals : Octachlorodibenzo-p-dioxin (OCDD) in fish.

According to present understanding, persistent superlipophilic chemicals - such as octachlorodibenzo-p-dioxin, octachlorodibenzofuran, Mirex etc - with log Kow > 6 and cross sections > 9.5 Å, bioconcentrate in aquatic organisms only little from ambient water. The most convincing argument against it is that in bioconcentration experiments with superlipophilic chemicals amounts applied exceeded water solubility by several orders of magnitude. This paper describes various methods for determining bioconcentration factors (BCF) of superlipophilic compounds. As exemplified with octachlorodibenzo-p-dioxin, BCF values evaluated by these methods match well with those calculated by QSARs for fish and mussels based on log Kow and water solubility. As expected, these BCF values exceed previous values by several orders of magnitude. For BCF evaluation of superlipophilic chemicals in aquatic organisms we recommend: (i) flow-through systems, kinetic method (OECD guideline No. 305 E) (ii) ambient concentrations < water solubility (iii) during the uptake and especially during the elimination phase no toxic effects of the test organisms should occur.

A review of the relationship between acute toxicity (LC50) of gamma-hexachlorocyclohexane (gamma-HCH, Lindane) and total lipid content of different fish species.

This paper provides an explanation for a 40-fold difference in the acute toxicity (LC50) of gamma-hexachlorocyclohexane (gamma-HCH, Lindane) in 14 different fish species, based on well recognized principles of toxicokinetics and toxicodynamics in combination with a compilation of data from the literature and some original data. The 48-h median lethal concentration (48-h LC50) of gamma-HCH in 14 fish species, belonging to 6 families, range from 22 to 900 micrograms/l. A significant positive linear relationship was found between lipid content (% of wet weight) and the 48-h LC50 of gamma-HCH in these fish species, revealing that the toxicity of gamma-HCH in various fish species is decreasing with increasing total lipid content. If median lethal concentrations are normalized for 1% lipid content, then the range of 48-h LC50s is reduced to between 18 and 32 micrograms/l. It is concluded that lipids of aquatic organisms can serve (among other functions) as a protective storage site against the toxic effects of gamma-HCH and, possibly, of other lipophilic, persistent organic chemicals which are bioconcentrated in body lipids. Therefore, in organisms with higher lipid content, a smaller fraction of a lipophilic chemical will reach target organs (liver, lung, central and peripheral nerves, etc.) to cause adverse effects. Results suggest that this correlation can be used to extrapolate the acute toxicity (48-h LC50) of gamma-HCH to other fish species if their lipid content is known. Furthermore, the data generated by extrapolation of this correlation could be useful in the environmental risk assessment of freshwater and marine organisms.

The relevance of fat content in toxicity of lipophilic chemicals to terrestrial animals with special reference to dieldrin and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

Lipophilic chemicals such as chlorinated hydrocarbon insecticides and other persistent chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are fat soluble chemicals and are readily bioconcentrated in animal fat depots. The modifying role of the body fat content in the toxicity of chlorinated cyclodiene insecticides to insects and in the toxicity of TCDD to different mammals was investigated. The single oral acute 30-day LD50 data of TCDD in different mammals are presented and correlated with their total body fat content. A two linear regression equation with log/log values was obtained. It is concluded that the storage of TCDD and other related lipophilic and persistent chemicals in lipids of organisms is, in a sense, a detoxication mechanism by which the compounds are removed from sites of action and/or receptors. Therefore, terrestrial organisms such as insects and mammals with higher total body fat content can accumulate and tolerate higher chlorinated hydrocarbon insecticide and TCDD doses than organisms with lower fat content. The different sensitivity of mammals of various species, strains, body weight, sex, age, etc. to acute toxicity of TCDD and related lipophilic persistent chemicals can mainly be explained by differences in total body fat content.

QSAR for organic chemical bioconcentration in Daphnia, algae, and mussels.

Prediction of the bioconcentration of organic chemicals from water by aquatic organisms has important applications in the management of hazardous chemicals. This study gives a compilation of bioconcentration factors on a wet weight basis (BCFw) of 52 organic chemicals by Daphnia magna from aqueous solution. The bioconcentration factors for the chemicals in Daphnia were successfully correlated with their n-octanol/water partition coefficients (log Kow) using a linear regression analysis. In addition to the ordinary least-square regression technique, the geometric mean regression technique is also used because this takes into account deviations in Kow values. Both results show that the Kow value of a chemical is a good predictor of the BCF in Daphnia. The BCF-Kow relationships between Daphnia, algae (Chlorella), and mussels (Mytilus edulis) are compared with each other.

Fate of [14C]monolinuron in potatoes and soil under outdoor conditions.

[phenyl-14C]Monolinuron was applied (2.5 and 1.9 kg/ha) to the soil surface of an outdoor lysimeter in two successive years: then, potatoes were grown. Total recovery of 14C in soil, plants, and leached water was about 55% (of 14C applied) after the first growing period and about 43% after the second growing period. Radioactivity in soil contained 77.1% (based on total 14C recovered in soil) bound residues, 15% monolinuron, and the following conversion products: N-(4-hydroxyphenyl)-N'-methoxy-N'-methylurea, N-(4-chlorophenyl)-N'-methylurea. N-(4-chlorophenyl)methylcarbamate, N-(4-chlorophenyl)-N-methyl-methylcarbamate, and 4-chloroformanilide. The leachate contained 0.8% (based on total 14C recovered in leachate) N-(4-hydroxyphenyl)-N'-methoxy-N'-methylurea. Potato plants contained 0.106 mg/kg radioactive residues in peeled tubers after one growing period and 15.94 mg/kg in the tops; after two growing periods, peeled tubers contained 0.091 mg/kg and tops contained 18.87 mg/kg radioactive residues. These residues consisted of bound 14C (57.9% of total 14C recovered in plants), N-(4-hydroxyphenyl)-N'-methoxy-N'-methylurea, N-(4-chlorophenyl)-N'-methylurea, N-(4-chlorophenyl)methylcarbamate, N-(4-chlorophenyl)-N-methyl-methylcarbamate, and 4,4'-dichlorozobenzene.

Kinetics of the uptake of 14C-labeled chlorinated benzenes from soil by plants.

[14C]Benzene, [14C]1,2,4-trichlorobenzene, [14C]pentachlorobenzene, and [14C]hexachlorobenzene were applied to soils in outdoor lysimeters to a 10-cm depth (2 mg/kg dry soil); barley and cress plants were grown for one vegetation period and analyzed after varying time intervals. The bioaccumulation factors (concentration of radioactive substances in plants divided by that in soils) of barley were higher than those of cress, except for hexachlorobenzene. In barley, bioaccumulation factors increased with decreasing chlorine content of the molecules, except for benzene, whereas in cress hexachlorobenzene exhibited the highest bioaccumulation factor. The conversion ratios of chlorinated benzenes (percentage of conversion products based on total radioactivity in plants) were negatively correlated to the chlorine content of the molecules and, in barley, positively correlated with time; in general, they were higher in barley than in cress. The concentration of radioactive substances in the plants, as well as bioaccumulation factors, decreased with time, except for a slight increase in benzene-derived residues in barley after 125 days. This effect is due to growth dilution. The percentage of radioactivity in barley seeds, based on that in the whole plant, was negatively correlated to the chlorine content of the molecule.

Bioconcentration potential of organic environmental chemicals in humans.

A list of environmental chemicals detectable in adipose tissue and/or milk of non-occupationally exposed humans is presented. Besides their physiochemical properties (n-octanol/water partition coefficient and water solubility), their acceptable daily intake (ADI) values, production figures, fate in the environment, concentrations in human adipose tissue, and data from total diet studies from market basket investigations are given. Average bioconcentration factors (BCF) of polychlorinated biphenyls (PCBs), 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), DDT, hexachlorobenzene (HCB), dieldrin, hexachlorocyclohexane isomers (alpha-HCH, beta-HCH, gamma-HCH, delta-HCH), pentachlorophenol (PCP), and 3,5-di-tert-butyl-4-hydroxytoluene (BHT) in human adipose tissue are calculated. The bioconcentration factors (wet wt basis) of these compounds are between 3 and 47 times higher in humans than in rats. The environmental chemicals are divided into three groups in respect to their bioconcentration factors in human adipose tissue: group I, high BCF (greater than 100); group II, medium BCF (10-100); and group III, low BCF (less than 10). The bioconcentration factors are useful for hazard assessment of chemicals to humans.

Comparison of methods to test chemicals for side effects on soil microorganisms.

The effects of the test chemicals pentachlorophenol (PCP) and HgCl2 on the bioactivity of microorganisms in three different soils were studied in low and high concentrations (2 and 20 ppm). Bioactivity was measured in long-term experiments (18 weeks) by a threefold application of chemicals to soils of varying moisture content. The selected tests were measurements of ATP, of heat output under aerobic and anaerobic conditions and after amendment with glucose, of soil respiration after the addition of glucose, and Fe(III) reduction. The suitability of each test depends on soil microorganisms, on environmental conditions, and on soil properties. The effects caused by the chemicals were as follows. For the low concentration, stimulation or inhibition were mostly repaired within the observation period. The high concentration mostly induced inhibitions which increased or decreased as a consequence of the repeated application of the chemicals. The effects of chemicals were strongly modified by the soil types: in a soil with high organic matter content, differences to the control were lower than in soils with lower organic matter content. These experiments also indicate that measurement of only one physiological parameter is not sufficient to characterize chemicals ecotoxicologically.