Abstract
Food Safety Commission of Japan (FSCJ) conducted a risk assessment of 2,4-D1) (CAS No. 94-75-7), a phenoxy herbicide, based on results from various studies. Major adverse effects of 2,4-D observed were suppressed body weight, renal tubular degeneration, hypertrophy of hepatocytes, reduced weight of testis and retinal degeneration in rats. No adverse effects were detected in carcinogenicity, reproductive toxicity, teratogenicity and genotoxicity relevant to human health. The relevant substance to the residue definition for dietary risk assessment was identified as 2,4-D and metabolite C2) in agricultural products and 2,4-D (parent compound only) in livestock products. The lowest no-observed-effect level (NOAEL) obtained from all the studies was 0.99 mg/kg bw/day in a two-year combined chronic toxicity/carcinogenicity study (the 1st study in Table 1) in rats. FSCJ specified an acceptable daily intake (ADI) of 0.0099 mg/kg bw/day by applying a safety factor of 100 to the NOAEL. The lowest NOAEL for adverse effects likely to be elicited by a single oral administration of 2,4-D was 15 mg/kg bw/day obtained from the acute neurotoxicity study in rats. Consequently, FSCJ specified an acute reference dose (ARfD) of 0.15 mg/kg bw by applying a safety factor of 100 to the NOAEL.
Conclusion in Brief
Food Safety Commission of Japan (FSCJ) conducted a risk assessment of 2,4-D1) (CAS No.94-75-7), a phenoxy herbicide, based on results from various studies.
The data used in the assessment include the fate in animals (rats, mice, goats, chickens and humans), fate in plants (paddy rice, wheat and others), residues in crops, acute neurotoxicity (rats), subacute toxicity (rats, mice and dogs), chronic toxicity (dogs), combined chronic toxicity/carcinogenicity (rats), carcinogenicity (mice), two-generation reproductive toxicity (rats), developmental toxicity (rats and rabbits), genotoxicity, and also on their mechanisms.
Major adverse effects of 2,4-D observed were suppressed body weight, renal tubular degeneration, hypertrophy of hepatocytes, reduced weight of testis and retinal degeneration in rats. No adverse effects were detected in carcinogenicity, reproductive toxicity, teratogenicity and genotoxicity relevant to human health.
Based on the results from various studies, the relevant substance to the residue definition for dietary risk assessment was identified as 2,4-D and metabolite C2) in agricultural products and 2,4-D (parent compound only) in livestock products.
The lowest no-observed-effect level (NOAEL) obtained from all the studies was 0.99 mg/kg bw/day in a two-year combined chronic toxicity/carcinogenicity study (the 1st study in Table 1) in rats. FSCJ specified an acceptable daily intake (ADI) of 0.0099 mg/kg bw/day by applying a safety factor of 100 to the NOAEL.
Table 1. Levels relevant to toxicological evaluation of 2,4-D .
| Species | Study | Dose (mg/kg bw/day) | NOAEL (mg/kg bw/day) and critical endpoints1) |
|---|---|---|---|
| Rat | 90-day subacute toxicity study (the 1st study) |
0, 1, 5, 15, 45 | M/F: 1 M/F: Renal lesion |
| 90-day subacute toxicity study (the 2nd study) |
0, 1, 15, 100, 300 M: 0, 0.93, 14.0, 93.9, 278 F: 0, 0.96, 14.4, 96.2, 293 |
M: 14.0 F: 14.4 M/F: Suppressed body weight, etc. |
|
| 90-day subacute toxicity study (the 3rd study) |
0, 15, 60, 100, 150 | M/F: 15 M/F: Renal tubular lesion, etc. |
|
| Two-year combined chronic
toxicity/carcinogenicity study (the 1st study) |
0, 1, 5, 15, 45 M: 0, 0.99, 4.95, 14.8, 44.5 F: 0, 0.99, 4.96, 14.9, 44.7 |
M/F: 0.99 M/F: Brown pigmentation of renal tubule, etc. (Not carcinogenic) |
|
| Two-year combined chronic
toxicity/carcinogenicity study (the 2nd study) |
0, 5, 75, 150 M: 0, 4.77, 73.2, 145 F: 0, 4.89, 73.1, 144 |
M: 4.77 F: 4.89 M/F: Increase in ALP, etc. (Not carcinogenic) |
|
| One-year chronic neurotoxicity study | 0, 5, 75, 150 M: 0, 4.77, 73.2, 145 F: 0, 4.89, 73.1, 144 |
M: 4.77 F: 4.89 M/F: Suppressed body weight (No chronic neurotoxicity) |
|
| Two-generation reproductive toxicity study | 0, 5, 20, 80 PM: 0, 5.0, 20.1, 79.8 PF: 0, 5.0, 19.9, 78.5 F1M: 0, 5.0, 19.2 F1F: 0, 5.0, 20.2 |
Parent PM: 5.0 PF: 19.9 F1M: 5.0 F1F: 20.2 Offspring PM: 5.0 PF: 5.0 F1M: 5.0 F1F: 5.0 Parent M: Localized tubular degeneration in renal medulla F: Suppressed body weight, etc. Offspring: Lower body weight (No adverse effect on fertility) |
|
| Extended one-generation reproductive toxicity study | 0, 100, 300, 600(F)/800(M) ppm | P generation M: 16.6 (300 ppm) F: 40.2 (600 ppm) M: Increased absolute/relative renal weight, etc. F: No toxicity F1 generation M: 20.9 (300 ppm) F: 23.3 (300 ppm) M/F: Suppressed body weight (During lactation period) F1 generation F(Adult): Proximal tubular degeneration in kidney (No adverse effects on fertility, developmental neurotoxicity, and developmental immunotoxicity) |
|
| Developmental toxicity study (the 1st study) |
0, 12.5, 25, 50, 75, 88 | Maternal: 88 Fetus: 25 Maternal: No toxicity Fetus: Lower body weight, increased skeletal variations (lumbar rib, wavy rib), etc. (Not teratogenic) |
|
| Developmental toxicity study (the 2nd study) |
0, 8, 25, 75 | Maternal: 25 Fetus: 25 Maternal: Suppressed body weight Fetus: Increased skeletal variations (Not teratogenic) |
|
| Mouse | 90-day subacute toxicity study (the 1st study) |
0, 5, 15, 45, 90 | - M/F: Renal lesion |
| 90-day subacute toxicity study (the 2nd study) |
0, 1.0, 15.0, 100, 300 M: 0, 0.98, 14.7, 98.2, 293 F: 0, 0.99, 14.8, 98.9, 296 |
M: 14.7 F: 14.8 M: Decrease in T4 F: Decrease in Glu, etc. |
|
| Two-year carcinogenicity study (the 1st study) |
0, 1, 15, 45 M: 0, 0.98, 14.9, 44.8 F: 0, 1.00, 14.9, 44.8 |
M: 0.98 F: 14.9 M: Homogenous change of renal tublar epitherlium F: Increased absolute/relative renal weight (Not carcinogenic) |
|
| Two-year carcinogenicity study (the 2nd study) |
F: 0, 5, 150, 300 F: 0, 5.01, 150, 310 |
F: 5.01 F: Increased absolute/relative renal weight, etc. (Not carcinogenic) |
|
| Two-year carcinogenicity study (the 3rd study) |
M: 0, 5, 62.5, 125 M: 0, 5.0, 61.9, 129 |
M: 5.0 M: Proximal tubular degeneration/regeneration in kidney, etc. (Not carcinogenic) |
|
| Rabbit | Developmental toxicity study | 0, 10, 30, 90 | Maternal: 30 Fetus: 90 Maternal: Suppressed body weight, etc. Fetus: No toxicity (Not teratogenic) |
| Dog | 90-day subacute toxicity study (the 1st study) |
0, 0.3, 1, 3, 10 | M: 1 F: 3 M/F: Change of renal convoluted proximal tubule, etc. |
| 90-day subacute toxicity study (the 2nd study) |
0, 0.5, 1, 3.75, 7.5 M: 0, 0.5, 1.0, 3.8, 7.8 F: 0, 0.5, 1.0, 3.8, 7.7 |
M/F: 1.0 M/F: Suppressed body weight, etc. |
|
| One-year chronic toxicity study | 0, 1, 5, 10/7.5* M: 0, 1.0, 5.2, 8.2 F: 0, 1.0, 5.0, 7.9 *: In the 8th week after administration, the dose was cut to 7.5 mg/kg bw/day |
M/F: 1.0 M/F: Suppressed body weight, etc. |
|
| ADI (cRfD) | NOAEL: 0.99 SF: 100 ADI: 0.0099 |
||
| The critical study for setting ADI | Two-year combined chronic toxicity/carcinogenicity study in rats (the 1st study) | ||
M, Male; F, Female; M/F, both sexes; PM, Male in P (Parent) generation; PF, Female in P generation;
F1M, Male in F1 generation; F1F, Female in F1 generation; -, NOAEL could not be specified; ADI, Acceptable daily intake;
cRfD, Chronic reference dose; SF, Safety factor; UF, Uncertainty factor; NOAEL, No-observed-adverse-effect level;
NOEL, No-observed-effect level; -, NOAEL could not be specified
1) The adverse effect observed at the lowest-observed-adverse-effect level (LOAEL)
The lowest NOAEL for adverse effects likely to be elicited by a single oral administration of 2,4-D was 15 mg/kg bw/day obtained from the acute neurotoxicity study in rats. Consequently, FSCJ specified an acute reference dose (ARfD) of 0.15 mg/kg bw by applying a safety factor of 100 to the NOAEL.(table 2-4)
Table 2. Potential adverse effects of a single oral administration of 2,4-D .
| Species | Study | Dose (mg/kg bw/day) |
NOAEL (mg/kg bw/day) and critical endpoints1) |
|---|---|---|---|
| Rat | Acute toxicity study | 0, 197(M), 250, 318, 403, 512, 650, 826 | M/F: - M/F: Hypoactivity, abnormal gait (1 hour after the treatment) |
| Acute neurotoxicity study | 0, 15, 75, 250 | M: 75 F: 15 M: Motor coordination ataxia, abnormal gait, decreased locomotor activity (5–6 hours after the treatment) F: Abnormal gait (5–6 hours after the treatment) |
|
| Mouse | General pharmacology study (General state) | 0, 30, 100, 300 | 30 Abnormal/atatic gait (0.5–5 hours after the treatment) |
| Acute toxicity study | 0, 200, 264, 348, 460, 670, 801 | M/F: - M/F: Hypoactivity, abnormal gait (1 hour after the treatment) |
|
| Rabbit | General pharmacology study (General state) | M:0, 30, 100, 300 | M: 100 Abnormal gait, decreased locomotor activity (3–4 hours after the treatment) |
| General pharmacology study (Body temperature) | M:0, 30, 100, 300 | M: 100 Elevated body temperature (2–3 hours after the treatment) |
|
| ARfD | NOAEL: 15 SF: 100 ARfD: 0.15 |
||
| The critical study for setting ARfD | Acute neurotoxicity study in rats | ||
ARfD, Acute reference dose; SF, Safety factor; NOAEL, No-observed-adverse-effect level; -, NOAEL or LOAEL could not be specified
1) The adverse effect observed at LOAEL
Table 3. Levels relevant to toxicological evaluation of 2,4-D .
| Species | Study | Test substances | Dose (mg/kg bw/day) |
NOAEL(mg/kg bw/day) and critical endpoints1) |
|---|---|---|---|---|
| Rat | 90-day subacute toxicity study | DEA salt | 0, 1.5, 27, 150, 440 [0, 1, 18, 100, 300] |
27 [18] Elevated mortality rate,etc. |
| DMA salt | 0, 1.2, 18, 120, 360 [0, 1, 15, 100, 300] |
18 [15] Suppressed body weight, etc. |
||
| IPA salt | 0, 1, 19, 130, 380 [0, 1, 15, 100, 300] |
19 [15] Suppressed body weight, etc. |
||
| TIPA salt | 0, 2, 28, 190, 560 [0, 1, 15, 100, 300] |
28 [15] Histopathological change in kidney, etc. |
||
| BEH ester | 0, 1.5, 22, 140, 440 [0, 1, 15, 100, 300] |
22 [15] Suppressed body weight, etc. |
||
| EH ester | 0, 1.5, 23, 150, 450 [0, 1, 15, 100, 300] |
23 [15] Suppressed body weight, etc. |
||
| Developmental toxicity study | DEA salt | 0, 15, 75, 150 [0, 11, 55, 110] |
Maternal: 15 [11] Fetus: 15 [11] Maternal: Suppressed body weight Fetus: Increased skeletal variations (Not teratogenic) |
|
| DMA salt | [0, 12, 50, 100] | Maternal: [12] Fetus: [50] Maternal: Suppressed body weight Fetus: Lower body weight, etc. (Not teratogenic) |
||
| IPA salt | 0, 22, 65, 190 [0, 9, 25, 74] |
Maternal: 65 [25] Fetus: 190 [74] Maternal: Suppressed body weight, etc. Fetus: No toxicity (Not teratogenic) |
||
| TIPA salt | 0, 32, 100, 320 [0, 12, 37, 120] |
Maternal: 100 [37] Fetus: 32 [12] Maternal: Death, etc. Fetus: Increase in skeletal variations |
||
| BEH ester | 0, 25, 75, 180 [0, 17, 50, 120] |
Maternal: 75 [50] Fetus: 75 [50] Maternal: Suppressed body weight Fetus: Delayed ossification (Not teratogenic) |
||
| EH ester | [0, 10, 30, 90] | Maternal: [30] Fetus: [30] Maternal: Suppressed body weight, etc. Fetus: Delayed ossification (Not teratogenic) |
||
| Rabbit | Developmental toxicity study | DEA salt | [0, 15, 30, 60] | Maternal: [15] Fetus: [30] Maternal: Suppressed body weight, etc. Fetus: Increased skeletal variations (Not teratogenic) |
| DMA salt | [0, 10, 30, 90] | Maternal: [30] Fetus: [90] Maternal: Reduced motor activity, etc. Fetus: No toxicity (Not teratogenic) |
||
| IPA salt | 0, 13, 38, 95 [0, 10, 30, 75] |
Maternal: 13 [10] Fetus: 95 [75] Maternal: Death, etc. Fetus: No toxicity (Not teratogenic) |
||
| TIPA salt | 0, 19, 56, 140 [0, 10, 30, 75] |
Maternal: 19 [10] Fetus: 140 [75] Maternal: Death, etc. Fetus: No toxicity (Not teratogenic) |
||
| BEH ester | 0, 15, 45, 110 [0, 10, 30, 75] |
Maternal: 15 [10] Fetus: 110 [75] Maternal: Death, etc. Fetus: No toxicity (Not teratogenic) |
||
| EH ester | [0, 10, 30, 75] | Maternal: [30] Fetus: [75] Maternal: Death, etc. Fetus: No toxicity (Not teratogenic) |
||
| Dog | 90-day subacute toxicity study | DMA salt | [0, 1, 3.8, 7.5] | M/F: [1] M/F: Suppressed body weight, etc. |
| EH ester | [0, 1, 3.8, 7.5] | M/F: [1] M/F: Suppressed body weight, etc. |
The values given in parentheses [ ] are the corresponding values in acid
DEA, dethanolamine; DMA, dimethylamine; IPA, Isopropylamine; TIPA, Triisopropanolamine; BEH, butoxyethyl; EH, ethylhexyl
1) The adverse effect observed at LOAEL
Table 4. Potential adverse effects of a single oral administration of 2,4-D .
| Test substances | Species | Study | Dose (mg/kg bw/day) |
NOAEL (mg/kg bw/day) and critical endpoints1) |
|---|---|---|---|---|
| 2,4-D ethyl | Rat | Acute toxicity study | 250, 350, 500 | M/F: - M/F: Hypoactivity, etc. (1 hour after the treatment) |
| Mouse | Acute toxicity study | 0, 125, 250, 290(M), 335(M), 375, 500 | M/F: - M/F: Hypoactivity, fece/soil (1 hour after the treatment) |
|
| Na salt | Rat | Acute toxicity study | 250, 500, 1 000, 2 000 | M/F: - M/F: Ataxia, hypoactivity, etc. (1 hour after the treatment) |
| Mouse | Acute toxicity study | 125, 250, 375, 500, 1 000 | M: - F: 125 M/F: Hypoactivity, etc. (1 hour after the treatment) |
|
| DMA salt | Rat | Acute toxicity study | 500, 710, 1 000 | M/F: - M/F: Ataxia, hypoactivity, etc. (1 hour after the treatment) |
| Mouse | Acute toxicity study | 250, 500, 1 000, 2 000, 4 000 | M/F: - M/F: Hypoactivity, ataxia, etc. (1 hour after the treatment) |
|
| IPA salt | Rat | Acute toxicity study | 500, 750, 1 000, 5 000 | M/F: - M/F: Stiffness in handling (1 day after the treatment) |
| DEA salt | Rat | Developmental toxicity study |
0, 15, 75, 150 [0, 11, 55, 110] |
Maternal: 15 [11] Maternal: Suppressed body weight (6–9 days after GD) |
| TIPA salt | Rat | Developmental toxicity study |
0, 32, 100, 320 [0, 12, 37, 120] |
Maternal: 100 [37] Embryo/fetus: 32 [12] Maternal: Death, rigid limbs, salivation, suppressed body weight (During the treatment) Embryo/fetus: Increased skeletal variation (wavy rib) |
| BEH ester | Rat | Developmental toxicity study |
0, 25, 75, 180 [0, 17, 50, 120] |
Maternal: 75 [50] Maternal: Suppressed body weight (6–9 days after GD) |
| EH ester | Rat | Developmental toxicity study |
[0, 10, 30, 90] | Maternal: [30] Maternal: Suppressed body weight (6–9 days after GD) |
The values given in parentheses [ ] are the corresponding values in acid
GD, gestation day; Na salt, sodium salt; other abbreviation are described in Table3.
1) The adverse effect observed at LOAEL
Acknowledgement:
FSCJ wishes to thank the members of Expert Committee on Pesticides for the preparation of the original full report.
This is an English translation of excerpts from the original full report (May 2017−FS/333/2017). Only original Japanese texts have legal effect. The original full report is available in Japanese at http://www.fsc.go.jp/fsciis/attachedFile/download?retrievalId=kya20130612152&fileId=201
References
- 1.2,4-dichlorophenoxy acetic acid.
- 2.2,4-dichlorophenol.