Paclobutrazol (Ref: PP 333)

Paclobutrazol (Ref: PP 333)	Last updated: 25/02/2021
(Also known as: paclobutrazole)

GENERAL INFORMATION

Description

A conazole plant growth regulator with some fungicidal activity for ornamentals, fruit and other crops to inhibit vegetative growth

Example pests controlled

Vegetative growth - cell division

Example applications

Mango; Cotton; Corn; Chilli; Bonzi production; Grape vines

Efficacy & activity

Availability status

Current

Introduction & key dates

1986

UK regulatory status

UK COPR regulatory status

Approved

Date COPR inclusion expires

31/05/2024

UK LERAP status

None

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Approved

Dossier rapporteur/co-rapporteur

UK/Romania

Date EC 1107/2009 inclusion expires

31/05/2021

EU Candidate for substitution (CfS)

Yes - two 'Persistent-Bioaccumulative-Toxic' criteria

Listed in EU database

Yes

Approved for use (✓) under EC 1107/2009 in the following EU Member States

ATAustria	BEBelgium	BGBulgaria	CYCyprus	CZCzech Republic	DEGermany	DKDenmark	EEEstonia	ELGreece
✓	✓	✓		✓	✓	✓	✓
ESSpain	FIFinland	FRFrance	HRCroatia	HUHungary	IEIreland	ITItaly	LTLithuania	LULuxembourg
✓	✓	✓		✓	✓	✓	✓
LVLatvia	MTMalta	NLNetherlands	PLPoland	PTPortugal	RORomania	SESweden	SISlovenia	SKSlovakia
✓		✓			✓	✓		✓

Also used in

Australia

Chemical structure

Isomerism

A molecule with two chiral centres. The technical material is a racemate comprising equimolar amounts of (2R,3R)- and (2S,3S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol.

Chemical formula

C₁₅H₂₀ClN₃O

Canonical SMILES

CC(C)(C)C(C(CC1=CC=C(C=C1)Cl)N2C=NC=N2)O

Isomeric SMILES

CC(C)(C)[C@H]([C@@H](CC1=CC=C(C=C1)Cl)N2C=NC=N2)O

International Chemical Identifier key (InChIKey)

RMOGWMIKYWRTKW-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/2C15H20ClN3O/c2*1-15(2,3)14(20)13(19-10-17-9-18-19)8-11-4-6-12(16)7-5-11/h2*4-7,9-10,13-14,20H,8H2,1-3H3/t2*13-,14-/m10/s1

2D structure diagram/image available?

Yes

General status

Pesticide type

Plant growth regulator; Fungicide

Substance group

Triazole

Minimum active substance purity

930 g kg⁻¹

Known relevant impurities

EU dossier - None declared

Substance origin

Synthetic

Mode of action

Absorbed through leaves, stem and roots and translocated

CAS RN

76738-62-0

EC number

266-325-7

CIPAC number

445

US EPA chemical code

125601

PubChem CID

158076

Molecular mass

293.8

PIN (Preferred Identification Name)

IUPAC name

(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol

CAS name

(αR,βR)-rel-β-((4-chlorophenyl)methyl)-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol

Other status information

Relevant Environmental Water Quality Standards

Herbicide Resistance Classification (HRAC)

Not applicable

Herbicide Resistance Classification (WSSA)

Not applicable

Insecticide Resistance Classification (IRAC)

Not applicable

Fungicide Resistance Classification (FRAC)

Not applicable

Examples of recorded resistance

Physical state

White crystalline solid

Related substances & organisms

propylene glycol

Formulations

Property

Value

Example manufacturers & suppliers of products using this active now or historically

Bonzi
Cultar
Parlay
Piroutte

Example products using this active

Agrovista
Fine
Syngenta

Formulation and application details

Often supplied as a suspension concentrate that is mixed with water and used as a spray

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

22.9

Low

Solubility - In organic solvents at 20 °C (mg l⁻¹)

72400

Acetone

5670

Xylene

150000

Methanol

199

n-Heptane

Melting point (°C)

164

Boiling point (°C)

384

Degradation point (°C)

Flashpoint (°C)

Not expected to self ignite; Not highly flammable

Octanol-water partition coefficient at pH 7, 20 °C

1.29 X 10⁰³

Calculated

Log P

3.11

High

Bulk density (g ml⁻¹)

1.23

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

0.0019

Low volatility

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

2.39 X 10^-05

Non-volatile

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Neutral solution: 222nm = 10900, 260nm = 233, 267nm = 294, 276nm = 236
Acidic solution: 221nm = 17500, 260nm = 228, 267nm = 284, 276nm = 229
Basic solution: 221nm = 12800, 260nm = 222, 267nm = 280, 276nm = 225
No absorbance > ca 280nm

Surface tension (mN m⁻¹)

66.0

at 20.5 °C]

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

112

Persistent

DT₅₀ (lab at 20 °C)

120

Persistent

DT₅₀ (field)

29.5

Non-persistent

DT₉₀ (lab at 20 °C)

577.5

Very persistent

DT₉₀ (field)

98.1

DT₅₀ modelling endpoint

Note

EU dossier lab studies DT₅₀ range 27.1-618 days (normalised), DT₉₀ range 143-2053 days, field studies DT₅₀ range 27.2-60.8 days (normalised), DT₉₀ range 46.7-202 days; Other studies: DT₅₀ (1) lab 84-140 days, field 6-13 months (B4), (2) US sources: 200 days (DW4)

Dissipation rate RL₅₀ on plant matrix

Value

4.4

Note

Wheat, whole plant, n=1

Dissipation rate RL₅₀ on and in plant matrix

Value

6.0

Note

OSR, whole plant, n=1

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Stable

Note

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Stable

Note

Stable pH 4 to pH 9 over 30 days at 25 °C

Water-sediment DT₅₀ (days)

787

Stable

Water phase only DT₅₀ (days)

164

Stable

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d

Moderately mobile

K_oc

400

Notes and range

Freundlich

K_f

4.3

Moderately mobile

K_foc

210

¹/_n

0.93

Notes and range

EU dossier kf range 0.68-15.1 mL g⁻¹, K_foc range 34.7-665.3 mL g⁻¹, ¹/_n range 0.87-0.97, Soils=13

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

2.47

Calculated

Transition state

SCI-GROW groundwater index (μg l⁻¹) for a 1 kg ha⁻¹ or 1 l ha⁻¹ application rate

Value

1.33 X 10^-01

Calculated

Note

Potential for particle bound transport index

Medium

Calculated

Potential for loss via drain flow

Moderately mobile

Calculated

Key metabolites

Metabolite

Formation medium

Estimated maximum occurrence fraction

1107/2009 relevancy

(2RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-one (Ref: CGA 149907)

Soil

0.274

Major fraction, Relevant

1,2,4-triazole (Ref: CGA 71019)

Soil

0.03

Minor fraction, Relevant

1H-1,2,4-triazol-1-ylacetic acid (Ref: CGA 142856)

Soil

Not relevant

Other known metabolites

Metabolite name and reference

Aliases

Formation medium / Rate

Estimated maximum occurrence fraction

Metabolising enzymes

2-amino-3-1,2,4-triazole-1-yl-propionic acid (Ref: CGA 131013)

triazole alanine

Plant

3-hydroxy-1H-1,2,4-triazole, hydroxy triazole (Ref: NOA 457654)
Note: Potenial groundwater pollutant

Water/sediment; Soil

(2RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H, 1,2,4-triazole-1-yl)-1-hydroxy-pentan-3-one (Ref: R117117)

hydroxy ketone

Water/sediment

(2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H, 1,2,4-triazole-1-yl)pentan-1,3-diol (Ref: SYN 536408)

diol

Water/sediment

2-hydroxy-3-[1,2,4]-triazole-1-yl-propionic acid (Ref: CGA 205639)

triazole lactic acid

Plant

ECOTOXICOLOGY

Property

Value

Source; quality score; and other information

Interpretation

Bio-concentration factor

BCF (l kg⁻¹)

Low potential

CT₅₀ (days)

Not available

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

1336

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

2.5

Rat

High

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

> 117

Rat Reproductive NOAEL

Moderate

Birds - Acute LD₅₀ (mg kg⁻¹)

> 2100

Colinus virginianus

Low

Birds - Short term dietary (LC₅₀/LD₅₀)

> 2000 mg kg feed⁻¹

Colinus virginianus

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

118.6

Anas platyrhynchos

Moderate

Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

23.6

Lepomis macrochirus

Moderate

Fish - Chronic 21 day NOEC (mg l⁻¹)

3.3

Salmo gairdneri

Moderate

Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

33.2

Daphnia magna

Moderate

Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

0.32

Daphnia magna

Moderate

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic plants - Acute 7 day EC₅₀, biomass (mg l⁻¹)

0.0082

Lemna gibba

High

Non-target plants

58.3

Tomato
Seedling emergence, ER₅₀
as g ha⁻¹

Algae - Acute 72 hour EC₅₀, growth (mg l⁻¹)

7.2

Pseudokirchneriella subcapitata

Moderate

Algae - Chronic 96 hour NOEC, growth (mg l⁻¹)

Honeybees (Apis spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

> 40

Apis mellifera

Moderate

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

> 2

Apis mellifera

Moderate

Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Bumblebees (Bombus spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Mason bees (Osmia spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Other pollinators (1)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Other pollinators (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)

> 500

Eisenia foetida corr

Moderate

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)

0.845

Eisenia foetida corr

Moderate

Other soil macro-organisms

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Other arthropod (1)

LR₅₀ g ha⁻¹

16.7

48 hour
Aphidius rhopalosiphi

% Effect

Other arthropod (2)

LR₅₀ g ha⁻¹

1000

>, 7 day
Typhlodromus pyri

% Effect

Soil micro-organisms

Nitrogen mineralisation: No significant adverse effect at 77 days
Carbon mineralisation: No significant adverse effect at 21 days

Dose: 20 kg ha⁻¹

Mesocosm study data

NOEAEC mg l⁻¹

HUMAN HEALTH AND PROTECTION

General

Property

Value

Source; quality score; and other information

Interpretation

Threshold of Toxicological Concern (Cramer Class)

High (class III)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

1336

Rat

Moderate

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

3.13

Rat 4 hr (nose only)

Other Mammal toxicity endpoints

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

0.022

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

0.1

SF=100

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

0.1

SF=100

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

No unacceptable risks to bystanders identified

Occupational

No unacceptable risks to operators or other workers identified

MRLs

European

EU MRL pesticide database

Notes

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

0.1

EU Dir 89/778/EC limit; Calc MAC=300 µg l⁻¹

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

Harmful if inhaled or swallowed

Handling issues

Property

Value and interpretation

General

Not explosive or oxidising
IMDG Transport Code is usually 4.1
Flammable

CLP classification 2013

Health: H302, H312, H319, H332, H361
Environment: H400, H410
Handling: H228

EC Risk Classification

Reproduction risk category 3: R63
Xn - Harmful: R20/22
N - Dangerous for the environment: R51, R53

EC Safety Classification

S60, S61

WHO Classification

II (Moderately hazardous)

UN Number

Usually 1325

Waste disposal & packaging

Packaging Group II (medium danger)

TRANSLATIONS

Language

Name

English

paclobutrazol

French

paclobutrazol

German

Paclobutrazol

Danish

paclobutrazol

Italian

paclobutrazolo

Spanish

paclobutrazol

Greek

Polish

paklobutrazol

Swedish

Hungarian

paklobutrazol

Dutch

paclobutrazool

Record last updated:	25/02/2021
Contact:	aeru@herts.ac.uk
Please cite as:	Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242