Ultraviolet irradiation enhances the nitration of allergens.

Ultraviolet (UV) light is widely used for disinfection in indoor environments. Some wavelengths of UV light can produce high concentration of O3. UV irradiation combined with O3 may have great potential for nitration of allergens in the presence of NO2 in the air. In this study, the effects of UV irradiation on the nitration of three major indoor allergens including group Ⅰ allergens of house dust mite (Der p 1 and Der f 1) and group Ⅰ allergen of dog (Can f 1) in the presence of NO2 and O3 were investigated by analysis of the protein quantity, tyrosine, peptides, and nitration degree. The results showed that UV irradiation induced a significant increase in the quantity of 3-nitrotyrosine in the allergens from 0.4 ± 0.4 ng to 4.0 ± 0.8 ng. After 12 h of UV-O3 co-exposure, the total nitration degrees of the three allergens ranged from 0.1% to 0.5%, which were significantly higher than those after only O3 exposure (p < 0.05). The analysis of peptides revealed that the nitration of tyrosine was site-specific. The tyrosine Y231, which was adjacent to aspartic acid, posed the highest nitration degree of 41.1 ± 24.0% in Der p 1. The nitration degree of tyrosine Y162 was the highest (1.7 ± 0.1%) in Der f 1. Overall, this study demonstrated that UV irradiation enhanced the O3-related nitration of allergens in the air, which provides an experimental basis for the impact of daily disinfection behavior on allergens.

Tyrosine nitration enhances the allergenic potential of house dust mite allergen Der p 2.

Nitration of allergenic proteins caused by atmospheric pollutants O3 and NO2 may enhance their allergenic potential. In the study, the influence of nitration was investigated on the allergenicity of Der p 2, which is a main allergen from house dust mites and plays an important role in allergenic rhinitis and asthma. The results reveal that nitrated Der p 2 enhanced the IgE-binding capacity, upregulated the mRNA expression and release of IL-6 and IL-8 from bronchial epithelial cells, and induced higher levels of specific-IgE, TH2 cytokines and white blood cells in mice. Besides, nitrated Der p 2 caused more severe oxidative stress and allergenic symptoms in mice. It is concluded that nitration enhanced the allergenicity of Der p 2 through not only directly inducing higher amount of specific-IgE and stronger responses of TH2 cytokines, but also indirectly aggravating allergic symptoms by oxidative stress and adjuvant-like activation airway epithelial cells. The study suggests that the contribution of nitration to the promotion in allergenicity should not be ignored when precisely assessing the risk of house dust mite allergens in real environment.

Residual profiles and health risk of indoor allergens in China.

Exposure to indoor allergens is a principal risk factor for allergic diseases. However, most of the previous studies on indoor allergens focused on very limited kinds of allergens in China. Knowledge of the simultaneous exposure to multiple allergens is still lacking. In this study, the residual profiles of 8 allergens were investigated in 166 dust samples from 11 cities in China. The house dust mite allergens including Der p 1, Der f 1, and Der 2 were detected in the range of <0.02-283.83 µg/g dust. The concentrations of dog allergen Can f 1 and cat allergen Fel d 1 varied widely, from <0.84-22,896.46 µg/g dust for Can f 1 and from <0.02-6298.96 µg/g dust for Fel d 1. Cockroach allergen Bla g 2 was detected in 68% of the samples but at a low level with a maximum of 9.44 µg/g dust. Comparatively low detection frequencies were found for mouse allergen Mus m 1 as 37% and for fungi allergen Asp f 2 as 24%. The frequency of cleaning sheets/bedding was negatively correlated to the levels of house dust mite allergens. The presence of pets indoors was associated with higher levels of pet allergens and lower levels of house dust mite allergens and cockroach allergen. Risk evaluation reveals that at least 4 allergens were found in more than 80% of the rooms and more than 2 allergens with median/high risk were detected in 42% of the rooms, indicating that simultaneous exposure to multiple allergens is prevalent in China.

Enantiomer-specific burden of metalaxyl and myclobutanil in non-occupationally exposed population with evidence from dietary intake and urinary excretion.

Metalaxyl (MET) and myclobutanil (MYC) are two widely used chiral fungicides that may pose health risks to non-occupationally exposed populations. Here, the two fungicides were enantiomer-specific quantified in the dietary food and urine of residents in an Eastern China city, to determine the exposure and excretion of these contaminants in different populations. Results indicate that residues of MET and MYC varied with different food items at 0.42-0.86 ng/g fresh weight (FW) and 0.18-0.33 ng/g FW, respectively. In urine samples, the residual levels after creatinine adjusting (CR) ranged from 10.2 to 1715.4 ng/g CR for MET and were below the detection limit up to 320.7 ng/g CR for MYC. Significant age- and gender-related differences were separately found in urinary MET and MYC of different populations. Monte-Carlo simulations suggested that children had higher daily dietary intake (DDI) but lower urinary excretion (DUE) rates than youths, and thus may suffer higher body burdens. The residues of antifungally ineffective enantiomers (S-MET and R-MYC) were slightly higher than their antipodes in foods. Moreover, the enantiomer-selective urinary excretion resulted in higher retention of S-MET and R-MYC in the human body. Our results suggest that both dietary intake and urinary excretion should be enantiomer-specifically considered when assessing the exposure risk and body burden of chiral fungicides in the non-occupationally exposed population. Furthermore, substitutive application of enantiomer-enriched fungicide formulations can not only benefit the antifungal efficacy but also be safer for human health.

Site-specific tyrosine nitration of group 1 allergens of house dust mite Dermatophagoides farinae (Der f 1) and Dermatophagoides pteronyssinus (Der p 1) in indoor dusts.

Nitration can enhance the allergenicity of proteins. The nitration status of house dust mite (HDM) allergens in indoor dusts, however, remains to be elucidated. In the study, site-specific tyrosine nitration degrees of the two important HDM allergens Der f 1 and Der p 1 in indoor dust samples were investigated by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The measured concentrations of native and nitrated allergens in the dusts were in the range of 0.86-29 µg g-1 for Der f 1 and from below the detection limit to 29 µg g-1 for Der p 1. Site-specific analysis revealed that all ten tyrosine residues in Der f 1 and Der p 1 were nitrated to different degrees in the investigated samples. The preferred nitration sites were Y56 in Der f 1 and Y37 in Der p 1 with the nitration degrees of 7.6-84% and 17-96% among the detected tyrosine residues, respectively. The measurements reveal high site-specific nitration degrees for tyrosine in Der f 1 and Der p 1 detected in the indoor dust samples. Further investigations are required to find out if the nitration really aggravates the health effects of HDM allergens and if the effects are tyrosine site-dependent.

Species-specific bioaccumulation and risk prioritization of psychoactive substances in cultured fish.

Psychoactive substances are becoming new concern in environmental research with their increasing applications and the potential threats to fishery production as these substances could alter the behavior of fish and consequently affect the yield and quality of cultured fish. In this study, the accumulation and risk of twenty psychoactive substances were investigated in five species of cultured fish in Eastern China. The results showed that the total concentrations of these twenty psychoactive substances ranged from 0.15 to 0.92 ng mL-1 in the plasma among the five species of cultured fish with an order of perch > crucian carp > bighead carp > grass carp > silver carp. Diazepam (DIAZ) and methamphetamine (MAMP) were identified as the most frequently detected compounds, which were found in 100% and 93% of the samples with a median concentration of 0.15 and 0.12 ng mL-1 in the plasma, respectively. Although all of the psychoactive substances posed low or negligible risk, species-specific analysis of risk prioritization revealed that alprazolam, MAMP, temazepam and DIAZ exhibited the greatest potentials of hazard to all species of the cultured fish but with a species-dependent variation. These findings suggest that the adverse effects of psychoactive substances on fishery production, especially on different species, should be considered.

Accumulation and risk prioritization of psychoactive substances in the critically endangered Yangtze finless porpoise.

Psychoactive substances have been identified as a kind of emerging contaminants in aquatic environment and pose potential adverse effects on aquatic animals. Yangtze finless porpoise, a critically endangered species in China, is also facing the threat of psychoactive substances. In this study, the accumulation characteristics and risk prioritization of psychoactive substances were investigated in Yangtze finless porpoise collected from Poyang Lake (PYL) and Tian-E-Zhou Oxbow (TZO) in Yangtze River basin. The levels of psychoactive substances were detected in the range of below method detection limits (MDLs) to 98.4 ng/mL in the serum of Yangtze finless porpoise. Codeine (COD) and methamphetamine were identified as the major substances due to the highest residual levels with a median concentration of 0.72 ng/mL and 0.33 ng/mL, respectively. The total concentrations of psychoactive substances in the porpoise collected from TZO was significantly higher than those from PYL. Risk analysis based on effect ratio derived from the ratio of steady-state psychoactive substance serum concentration in the porpoise and human therapeutic plasma concentration revealed that COD was the substance with the highest risk among the psychoactive substances detected, followed by lysergic acid diethylamide (LSD), morphine, alprazolam (ALPZ) and lormetazepam. Location-specific risk prioritization of psychoactive substances found that the top 3 substances are LSD, lorazepam (LORZ) and ALPZ in PYL, and COD, LSD and LORZ in TZO. The results disclose the accumulation of psychoactive substances in Yangtze finless porpoise and suggest that the potential adverse effects should be concerned.

House dust mite allergens and nitrated products: Identification and risk assessment in indoor dust.

Air pollutants can potentially lead to nitration of allergic proteins, thus promoting sensitization of these allergens. However, little is currently known about the nitration status of house dust mite (HDM) allergens. We identified the occurrence of nitrated products of two major HDM allergens Der f 1 and Der p 1 in dust samples collected from college dormitories in eastern China and assessed their associated health risk. The results showed that both non-nitrated and nitrated forms of the two allergens were detected in the dust in the range of non-detected (ND)-10.6, 1.44-15.4, ND-22.4, ND-7.28 µg/g for non-nitrated Der f 1, nitrated Der f 1, non-nitrated Der p 1 and nitrated Der p 1, respectively. The median rates of nitration were determined as 74.0% for Der f 1 and 20.4% for Der p 1 at consideration of one nitration site. Further analysis reveals that the levels of HDM allergens and their nitrated products were found to be generally higher during winter, in dormitories of lower altitude and with female occupants. Furthermore, the calculated risk indexes were at considerably high levels. Our findings suggest that nitrated HDM allergens have already accumulated in the environment at such significant levels and their associated health risk calls for our immediate attention.

In Silico simulation of Cytochrome P450-Mediated metabolism of aromatic amines: A case study of N-Hydroxylation.

Aromatic amines, the widely used raw materials in industry, cause long-term exposure to human bodies. They can be metabolized by cytochrome P450 enzymes to form active electrophilic compounds, which will potentially react with nucleophilic DNA to exert carcinogenesis. The short lifetime and versatility of the oxidant (a high-valent iron (IV)-oxo species, compound I) of P450 enzymes prompts us to use theoretical methods to investigate the metabolism of aromatic amines. In this work, the density functional theory (DFT) has been employed to simulate the hydroxylation metabolism through H-abstraction and to calculate the activation energy of this reaction for 28 aromatic amines. The results indicate that the steric effects, inductive effects and conjugative effects greatly contribute to the metabolism activity of the chemicals. The further correlation reveals that the dissociation energy of -NH2 (BDEN-H) can successfully predict the time-consuming calculated activation energy (R2 for aromatic and heteroaromatic amines are 0.93 and 0.86, respectively), so BDEN-H can be taken as a key parameter to characterize the relative stability of aromatic amines in P450 enzymes and further to quickly assess their potential toxicity. The validation results prove such relationship has good statistical performance (qcv2 for aromatic and heteroaromatic amines are 0.95 and 0.90, respectively) and can be used to other aromatic amines in the application domain, greatly reducing computational cost and providing useful support for experimental research.

Behavioral changes and neurochemical responses in Chinese rare minnow exposed to four psychoactive substances.

With the increase use of psychoactive pharmaceuticals, these substances and their metabolites are frequently detected in aquatic environment. However, there is still a knowledge gap in the neurotoxicity of these pollutants on aquatic organisms as well as related behavioral effects. In this study, the effects of four psychoactive substances alprazolam (ALPZ), lorazepam (LORZ), codeine (COD) and morphine (MOR) were investigated on 23 neurochemicals and 5 behaviors in Chinese rare minnow (Gobiocypris rarus). The comprehensive neurotoxicity was then evaluated at three levels of neurochemical, neurotransmitter system and comprehensive index. The results indicated that ALPZ and LORZ not only increased serotonin and dopamine along with the decrease of glutamic acid, but also depressed the locomotory activity of Chinese rare minnow although without significance. Exposure to COD and MOR increased acetylcholine, dopamine and adrenaline, and significantly increased anxiety-related behaviors of Chinese rare minnow. Comprehensive evaluation showed that COD has the lowest neurotoxic effect on Chinese rare minnow. LORZ shows a stronger neurotoxicity at low concentration of exposure than the other three substances. MOR has the highest neurotoxic effect at high concentration of exposure among the four drugs. The findings revealed the comprehensive neurotoxicity of these psychoactive substances in fish and suggested ecological risks of these pollutants in aquatic environment.

Enantiomer/stereoisomer-specific residues of metalaxyl, napropamide, triticonazole, and metconazole in agricultural soils across China.

In this study, the residual status of four chiral pesticides including metalaxyl, napropamide, triticonazole, metconazole, and their enantiomers/stereoisomers were investigated in agricultural soils across China. The levels in the soils were detected as non-detected (n.d.)-16.67 ng/g for metalaxyl with a median of 0.14 ng/g; 0.004-32.99 ng/g for napropamide with a median of 0.29 ng/g; n.d.-207.39 ng/g for triticonazole with a median of 1.29 ng/g; and n.d.-71.83 ng/g for metconazole with a median of 1.03 ng/g, respectively. Enantiomer/stereoisomer-specific residues were observed for metalaxyl and triticonazole. R-Metalaxyl and R-triticonazole were identified as the major enantiomers in the soils for the two pesticides. There was no obvious enantioselective residue for napropamide in most of the soils. As for metconazole, metconazole-1 and metconazole-4 were identified as the major stereoisomers in the soils. These results suggest that enantiomer/stereoisomer-specific risk should be considered when assessing the ecological safety of these pesticides in soils.

Occurrence and risk assessment of psychoactive substances in tap water from China.

Psychoactive substances are becoming a new concern in aquatic environment along with the increase in use of these substances. In this study, 23 psychoactive substances were investigated in the tap water collected in 63 sites in China. Eighteen out of 23 psychoactive substances were detected at the range of < method detection limits (MDLs) to 24.9 ng L-1. It was found that diazepam and temazepam were the major psychoactive substances in the tap water with the median concentration of 1.0 and 0.06 ng L-1, respectively. The high exposure dose for each psychoactive substance was calculated from 0.6 to 855 pg kg-1 bw d-1 and showed an order of men ≥ boys ≥ girls ≥ women. Risk assessment revealed there was little risk of psychoactive substances on human health at current residual levels.

Integrated gender-related effects of profenofos and paclobutrazol on neurotransmitters in mouse.

This study investigated the effects of paclobutrazol and profenofos on six neurotransmitters and their metabolites involving in cholinergic and non-cholinergic neurotransmission systems in mouse. The results revealed that profenofos decreased the levels of 5-hydroxyindole-3-acetic acid (5-HIAA) and normetanephrine (MNE), and increased the level of dopamine (DA) in the mice after four weeks of exposure. The turnovers of serotonergic neurotransmission system (5-HIAA/5-HT) and noradrenergic neurotransmission system (MNE/NE) showed a decline under exposure of profenofos. Exposure to paclobutrazol resulted in decreases of 5-HIAA and MNE in both sexes of mice, and of 5-HT and ACh in the females. Similar to profenofos, the turnovers of serotonergic neurotransmission system and noradrenergic neurotransmission system decreased in the mice exposed to paclobutrazol. The integrated biomarker response (IBR) was introduced to comprehensively evaluate the neurotoxic effects of the two pesticides through integration of the responses of neurotransmitters. The results of IBR indicated that the overall effect of neurotransmitters increased at the beginning of exposure and then decreased in the end. It was also found that the order of neurotoxic effect for the two pesticides is as: paclobutrazol > profenofos referred to their LD50. Furthermore, the effects on neurotransmitters are higher in the males.

Urinary metabolites of organophosphate esters and implications for exposure pathways in adolescents from Eastern China.

Ten urinary biomarkers of organophosphate esters (OPEs) from six parent OPEs were analyzed in urine from adolescents students in Eastern China. Bis (1,3-dichloro-2-propyl) phosphate, urinary biomarker of tris (1,3-dichloro-2-propyl) phosphate (TDCIPP), was detected in all urine samples with the highest residual concentration of 6.2 ng/mL (median). Bis (1-chloro-propyl) hydroxyl-2-propyl phosphate, dibutyl phosphate, biomarkers of tris (1-chloro-2-propyl) phosphate (TCIPP), tri-n-butyl phosphate (TNBP), respectively, and tris (2-chloroethyl) phosphate (TCEP), were also frequently detected with median concentrations of 1.5, 2.6 and 0.3 ng/mL, respectively. Results indicate that exposure to OPEs, in particular to TDCIPP, TNBP, TCIPP and TCEP, was highly prevalent for adolescent students. The exposure pathways of OPEs were then evaluated according to the OPE internal body burdens (IBBs). Three pathways were identified as the main pathways for adolescents exposed to OPEs including dermal absorption, oral intake of food and dust and inhalation.

Metabolic Mechanism of Aryl Phosphorus Flame Retardants by Cytochromes P450: A Combined Experimental and Computational Study on Triphenyl Phosphate.

Understanding metabolic mechanisms is critical and remains a difficult task in the risk assessment of emerging pollutants. Triphenyl phosphate (TPHP), a widely used aryl phosphorus flame retardant (aryl-PFR), has been frequently detected in the environment, and its major metabolite was considered as diphenyl phosphate (DPHP). However, knowledge of the mechanism for TPHP leading to DPHP and other metabolites is lacking. Our in vitro study shows that TPHP is metabolized into its diester metabolite DPHP and mono- and dihydroxylated metabolites by cytochromes P450 (CYP) in human liver microsomes, while CYP1A2 and CYP2E1 isoforms are mainly involved in such processes. Molecular docking gives the conformation for TPHP binding with the active species Compound I (an iron IV-oxo heme cation radical) in specific CYP isoforms, showing that the aromatic ring of TPHP is likely to undergo metabolism. Quantum chemical calculations have shown that the dominant reaction channel is the O-addition of Compound I onto the aromatic ring of TPHP, followed by a hydrogen-shuttle mechanism leading to ortho-hydroxy-TPHP as the main monohydroxylated metabolite; the subsequent H-abstraction-OH-rebound reaction acting on ortho-hydroxy-TPHP yields the meta- and ipso-position quinol intermediates, while the former of which can be metabolized into dihydroxy-TPHP by fast protonation, and the latter species needs to go through type-I ipso-substitution and fast protonation to be evolved into DPHP. We envision that the identified mechanisms may give inspiration for studying the metabolism of several other aryl-PFRs by CYP.

Enantioselectivity in biotransformation and bioaccumulation processes of typical chiral contaminants.

Chirality is a critical topic in the medicinal and agrochemical fields. One quarter of all agrochemicals was chiral in 1996, and this proportion has increased remarkably with the introduction of new compounds over time. Despite scientists have made great efforts to probe the enantiomeric selectivity of chiral chemicals in the environment since early 1990s, the different behaviours of individual enantiomers in biologically mediated processes are still unclear. In the present review, we highlight state-of-the-knowledge on the stereoselective biotransformation and accumulation of chiral contaminants in organisms ranging from invertebrates to humans. Chiral insecticides, fungicides, and herbicides, polychlorinated biphenyls (PCBs), pharmaceuticals, flame retardants hexabromocyclododecane (HBCD), and perfluorooctane sulfonate (PFOS) are all included in the target compounds. Key findings included: a) Changes in the enantiomeric fractions in vitro and in vivo models revealed that enantioselectivity commonly occurs in biotransformation and bioaccumulation. b) Emerging contaminants have become more important in the field of enantioselectivity together with their metabolites in biological transformation process. c) Chiral signatures have also been regarded as powerful tools for tracking pollution sources when the contribution of precursor is unknown. Future studies are needed in order to understand not only preliminary enrichment results but also detailed molecular mechanisms in diverse models to comprehensively understand the behaviours of chiral compounds.

Estimation of soil-specific microbial degradation of alpha-cypermethrin by compound-specific stable isotope analysis.

In this study, the microbial degradation of alpha-cypermethrin was investigated in 14 different soil samples by compound-specific stable isotope analysis. After 40 and 80 days of microbial degradation, the stable carbon isotope ratios of alpha-cypermethrin shifted from - 32.18 to - 31.87‰ ~ - 31.12 and - 31.45‰ ~ - 29.75‰ in the soils, respectively. The microbial degradation percentages of alpha-cypermethrin were calculated as 15.6~44.3% after 40 days of incubation and 33.3~73.9% after 80 days of incubation. The effects of physicochemical properties of soil samples were then explored on the microbial degradation of alpha-cypermethrin. The results revealed that the microbial degradation percentages were positively correlated with the contents of organic carbon in soils with Pearson correlation coefficients of 0.794 and 0.843 for 40 and 80 days of microbial degradation, respectively, indicating that the microbial degradation of alpha-cypermethrin was faster in the soil with higher content of organic carbon. Accordingly, soil-specific use should be considered in practical agricultural application of alpha-cypermethrin to reduce the residue of the pesticide.

Status of mercury accumulation in agricultural soil across China: Spatial distribution, temporal trend, influencing factor and risk assessment.

Given its wide distribution in the natural environment and global transport potential, mercury (Hg) is regarded as a ubiquitous pollutant. In this study, we carried out nation-wide sampling campaigns across China to investigate the distribution of Hg in agricultural soils. Concentrations of Hg in the soils collected in 2011 and 2016 ranged from 0.04 to 0.69 and 0.06-0.78 mg kg-1, respectively. Based on the data from 2016, the reserve of Hg in the surface arable soils (0-20 cm) in China was 4.1 × 104 metric tons and Chinese cultivated soils accounted for 63.4-364 metric tons of Hg released to the global atmosphere. The soil Hg concentrations were significantly higher than the reference background level, highlighting the impacts of anthropogenic activities. The vertical distribution pattern showed a clear enrichment at the surface and a decrease with depth of the soils. Comparison of calculated geo-accumulation indexes among individual provinces showed that Northwest China had higher levels of Hg contamination than other regions of China, likely due to long-term energy related combustions in the area. Soil Hg level showed strong positive correlations with organic matter contents of soil, as well as the mean annual precipitation and temperature of the sampling locations. The non-carcinogenic human health risks of soil Hg were below the threshold level, but the general risk to the ecosystem was considerable. The increases in Hg accumulation from 2011 to 2016 at provincial level were found to relate to coal combustion, power generation and per capita GDP. This examination of energy consumption and socioeconomic drivers for China's soil Hg reserve increase is critical for direct Hg control by guiding policy-making and targets of technology development in era of rapid economic growth.

A new approach to estimate bioavailability of pyrethroids in soil by compound-specific stable isotope analysis.

In this study, the microbial degradation of six pyrethroids (bifenthrin, fenpropathrin, permethrin, α-cypermethrin, fenvalerate and deltamethrin) was investigated in soil to develop a new approach to estimate bioavailability of pyrethoids by compound-specific stable isotope analysis (CSIA). After 56-day incubation, the residual concentrations of pyrethroids in unsterilized soil were much lower than those in sterilized soil, indicating that microbial degradation was dominant for the elimination of pyrethroids. Meanwhile, the stable carbon isotope ratios of the six pyrethroids were determined during the degradation. Significant stable carbon isotope fractionation was observed during the microbial degradation of fenpropathrin, α-cypermethrin and deltamethrinhe. The enrichment factor ε was determined as -1.88‰, -1.82‰ and -2.00‰, respectively. A new approach was then developed to estimate the bioavailability of the three pyrethroids by determining stable carbon isotope ratios. The approach established in the study provides an alternative method to dynamically and quantitatively estimate bioavailability of compounds in soil based on CSIA.

CYP450 enzyme-specific enantioselective species-specific response for metalaxyl in in vitro hepatic cells.

Although enantioselective accumulation of chiral pesticide has been reported in organisms, the mechanisms remain unclear. In this study, the effects of chiral pesticide metalaxyl on CYP1A1, CYP1A2, CYP2B1, CYP2B2, CYP2E1 and CYP3A were investigated in human hepatoma HepG2, rat hepatic H4IIE, chicken hepatic LMH and grass carp hepatic L8824 cells. Moreover, the residual concentrations and enantiomeric ratios (ERs) of metalaxyl were also detected in the medium. The results showed the responses of these CYP450s to metalaxyl were enzyme-dependent and species-dependent in the four cells. CYP1A1, CYP1A2, and CYP2B1 were induced in HepG2 cells, CYP2A1 and CYP2B1 were induced in H4IIE cells, CYP1A1 and CYP2B1 were induced in LMH cells, and CYP2B1 was induced in L8824 cells. The enantioselective residual of metalaxyl was detected in the medium and found to be species-specific. HepG2, H4IIE and LMH cells were inclined to attenuate S-metalaxyl and lead to decrease of ER of metalaxyl, while L8824 cells were inclined to remove R-metalaxyl and resulted in an inverse shift of ER. These findings suggest an enantioselective metabolism of metalaxyl in various species which is not only related with CYP450s and CYP450 enzyme-specific, but also species-specific.