United States Environmental Office of Water EPA-822-R-05-006 

Protection Agency Office of Science and December 2005 

 Technology 4304T

 Aquatic Life Ambient 

Water Quality Criteria 

Diazinon 

FINAL 
ii

EPA-822-R-05-006 

Aquatic Life Ambient Water Quality Criteria 

Diazinon

(CAS Registry Number 333-41-5) 

FINAL

December 2005 

U.S. Environmental Protection Agency 

Office of Water 

Office of Science and Technology 

Washington, DC 
iii

NOTICE 

This document has been reviewed in accordance with U.S. EPA policy and approved for 

publication. Mention of trade names or commercial products does not constitute endorsement or 

recommendation for use. 

This document can be downloaded from EPA’s website at:

http://www.epa.gov/waterscience/criteria/aqlife.html
iv

FOREWORD 

 Section 304(a)(1) of the Clean Water Act of 1977 (P.L. 95-217) requires the Administrator 

of the Environmental Protection Agency to publish water quality criteria that accurately reflect 

the latest scientific knowledge on the kind and extent of all identifiable effects on health and 

welfare which might be expected from the presence of pollutants in any body of water, including 

ground water. This document is a revision of proposed criteria based on consideration of 

comments received from independent peer reviewers and the public. Criteria contained in this 

document replace any previously published EPA aquatic life criteria for the same pollutant(s). 

 The term “water quality criteria” is used in two sections of the Clean Water Act, section 

304(a)(1) and section 303(c)(2). The term has a different program impact in each section. In 

section 304, the term represents a non-regulatory, scientific assessment of health or ecological 

effects. Criteria presented in this document are such scientific assessments. If water quality 

criteria associated with specific waterbody uses are adopted by a state or tribe as water quality 

standards under section 303, they become enforceable maximum acceptable pollutant 

concentrations in ambient waters within that state or tribe. Water quality criteria adopted in state 

or tribal water quality standards could have the same numerical values as criteria developed 

under section 304. However, in many situations states or tribes might want to adjust water 

quality criteria developed under section 304 to reflect local environmental conditions and 

exposure patterns. Alternatively, states or tribes may use different data and assumptions than 

EPA in deriving numeric criteria that are scientifically defensible and protective of designated 

uses. It is not until their adoption as part of state or tribal water quality standards that criteria 

become regulatory. Guidelines to assist the states and tribes in modifying the criteria presented 

in this document are contained in the Water Quality Standards Handbook (U.S. EPA 1994). The 

handbook and additional guidance on the development of water quality standards and other 

water-related programs of this agency have been developed by the Office of Water. 

 This final document is guidance only. It does not establish or affect legal rights or 

obligations. It does not establish a binding norm and cannot be finally determinative of the 

issues addressed. Agency decisions in any particular situation will be made by applying the 

Clean Water Act and EPA regulations on the basis of specific facts presented and scientific 

information then available. 

 Ephraim King, Director 

 Office of Science and Technology 
v

ACKNOWLEDGMENTS 

Document Authors 

Larry T. Brooke 

University of Wisconsin-Superior 

Superior, WI 

Gregory J. Smith 

Great Lakes Environmental Center 

Columbus, OH 

U.S. EPA Document Coordinators 

Heidi Bell Office of Water 

Rick Stevens Office of Water 

U.S. EPA Technical Reviewers 

Tala Henry Office of Water 

Walter Berry Office of Research and Development 

Cindy Roberts Office of Research and Development 

Robert Spehar Office of Research and Development 

Thomas Steeger Office of Prevention, Pesticides and Toxic Substances 

Charles Stephan Office of Research and Development 

Glen Thursby Office of Research and Development 
vi

TABLE OF CONTENTS

NOTICE........................................................................................................................................iii 

FOREWORD................................................................................................................................ iv 

ACKNOWLEDGMENTS ............................................................................................................ v 

FIGURES..................................................................................................................................... vii 

TABLES....................................................................................................................................... vii 

1. INTRODUCTION................................................................................................................. 1 

1.1. Physical-Chemical Properties...................................................................................... 1 

1.2. Diazinon in the Environment....................................................................................... 2 

1.3. Toxicity of Diazinon...................................................................................................... 4 

1.4. Derivation of Aquatic Life Ambient Water Quality Criteria ................................... 5 

2. ACUTE TOXICITY TO AQUATIC ANIMALS............................................................... 6 

2.1. Freshwater..................................................................................................................... 6 

2.2. Saltwater ........................................................................................................................ 7 

3. CHRONIC TOXICITY TO AQUATIC ANIMALS ......................................................... 9 

3.1. Freshwater..................................................................................................................... 9 

3.2. Saltwater ...................................................................................................................... 11 

3.3. Acute-Chronic Ratios ................................................................................................. 11 

4. TOXICITY TO AQUATIC PLANTS............................................................................... 13 

5. BIOACCUMULATION ..................................................................................................... 14 

6. OTHER DATA.................................................................................................................... 15 

6.1. Freshwater................................................................................................................... 15 

6.2. Saltwater ...................................................................................................................... 20 

6.3. Olfactory Effects of Diazinon in Aquatic Organisms .............................................. 21 

7. UNUSED DATA.................................................................................................................. 23 

8. SUMMARY ......................................................................................................................... 26 

8.1. Freshwater Data.......................................................................................................... 26 

8.2. Saltwater Data............................................................................................................. 26 

8.3. Plant Data .................................................................................................................... 27 

8.4. Bioaccumulation Data ................................................................................................ 27 

9. NATIONAL CRITERIA.................................................................................................... 28 

9.1. Freshwater................................................................................................................... 28 

9.2. Saltwater ...................................................................................................................... 28 

10. IMPLEMENTATION .................................................................................................... 29 

11. REFERENCES................................................................................................................ 60 
vii

FIGURES

Page

Figure 1. Summary of Ranked Diazinon GMAVs (Freshwater) ..................................................30 

Figure 2. Summary of Ranked Diazinon GMAVs (Saltwater).....................................................31 

Figure 3. Chronic Toxicity of Diazinon to Aquatic Animals .......................................................32 

TABLES

Table 1. Acute Toxicity of Diazinon to Aquatic Animals............................................................33 

Table 2. Chronic Toxicity of Diazinon to Aquatic Animals.........................................................40 

Table 3. Ranked Genus Mean Acute Values with Species Mean Acute-Chronic Ratios.............42 

Table 4. Toxicity of Diazinon to Aquatic Plants ..........................................................................46 

Table 5. Bioaccumulation of Diazinon by Aquatic Organisms ....................................................47 

Table 6. Other Data on Effects of Diazinon on Aquatic Organisms ............................................48 
1

1. INTRODUCTION 

1.1. Physical-Chemical Properties 

 Diazinon [Chemical Abstract Service registry number 333-41-5; O,O-diethyl O-(6-methyl2-{1-methylethyl}-4-pirimidinyl) phosphorothioate] is a broad spectrum insecticide effective 

against adult and juvenile forms of flying insects, crawling insects, acarians and spiders (WHO 

1998). Specific uses include the control of pest insects such as cutworms, wireworms, and 

maggots in soil (Farm Chemicals Handbook 2000) and ectoparasites on sheep (Virtue and 

Clayton 1997). It is also effective against many pests of fruits, vegetables, tobacco, forage, field 

crops, range, pasture, grasslands and ornamentals. Additional diazinon uses in urban areas 

include dormant sprays on fruit trees, professional landscape and maintenance, and structural 

pest control (Bailey et al. 2000). Until recently, most diazinon was used in and around the home 

and in other non-agricultural settings including treatment of lawns, gardens, and ornamentals, 

and indoor crack and crevice treatment. After December 31, 2004, it became unlawful to sell 

outdoor, non-agricultural diazinon products in the United States (i.e., all residential uses of the 

insecticide diazinon have been cancelled). However, it is lawful to use diazinon for nonresidential agricultural or other uses in accordance with product labeling and precautions 

approved by EPA under the Federal Insecticide, Fungicide and Rodenticide Act. 

 Diazinon is an organophosphorus compound with the empirical formula of C12H21N2O3PS, 

a molecular weight of 304.35 g/mole and has a log octanol/water partition coefficient (log Kow) 

of 3.40 (Hunter et al. 1985; WHO 1998). In its purest form diazinon is a colorless oil with a 

density greater than water (1.116-1.118 g/mL at 20°C) and is soluble in water at 20°C to 0.006 

percent (40 mg/L, Farm Chemicals Handbook 2000; 40.5 mg/L, Kanazawa 1983b; 60 mg/L, 

WHO 1998). The technical product is a pale to dark brown liquid of at least 90 percent purity 

and has a faint ester-like odor. Diazinon decomposes above 120°C (Verschueren 1983, WHO 

1998), is susceptible to oxidation above 100°C, is stable in neutral media, but slowly hydrolyzes 

in alkaline media and more rapidly in acidic media (WHO 1998). If stored properly, diazinon 

has a shelf-life of at least three years (SOLARIS Consumer Affairs for Ortho products, P.O. Box 

5008, San Ramos, CA 94583, 1998). 

 Commercial formulations of diazinon previously contained the impurity sulfotepp 

(O,O,O,O-tetraethyl dithiopyrophosphate), but current diazinon formulations produced by 
2

Makhteshim - Agan of North America do not contain sulfotepp (personal communication, 

Makhteshim - Agan of North America, 2004). Historically, sulfotepp was found at levels 

ranging from 0.20 to 0.71 percent of the diazinon concentrations (Meier et al. 1979). Allender 

and Britt (1994) conducted a screening program throughout Australia to determine the degree of 

breakdown products in diazinon formulations. Of the 169 samples evaluated, eight contained the 

degradates, O,S-TEPP and S,S-TEPP. The presence of the sulfotepp degradates was directly 

correlated with the presence of water in the container. Sulfotepp is more stable than diazinon 

and therefore should persist longer in the environment. It should be noted that sulfotepp is also 

used alone as a pesticide, marketed under the trade names ASP-47 and Bladafun by the Bayer 

Corporation for fumigation control in greenhouse crops and mushrooms (Agrochemicals 

Handbook 1991). 

1.2. Diazinon in the Environment 

 Diazinon has been detected in freshwater (Bailey et al. 2000; Domagalski et al. 1997; Land 

and Brown 1996; Lowden et al. 1969; McConnell et al. 1998; Ritter et al. 1974). 

Organophosphorus pesticides, including diazinon, were found in almost all samples of seawater, 

but not in net plankton from the harbor of Osaka City, Japan (Kawai et al. 1984). Kawai et al. 

(1984) reported diazinon was applied from June to August to rice paddy fields resulting in 

concentrations in the Osaka City harbor greater than 0.1 μg/L. 

 Diazinon has been detected in point source (e.g., wastewater treatment plant effluents) 

discharges (Villarosa et al. 1994). U.S. EPA’s National Effluent Toxicity Assessment Center 

investigated the occurrence of diazinon in 28 different publicly owned treatment works (POTW) 

effluents located across the country in 1988. Detectable levels were found in samples from 17 of 

the 28 facilities, primarily those located in southern states (Norberg-King et al. 1989). The 

authors concluded that the diazinon levels found in several effluents were sufficiently high to be 

a contributing factor to the toxicity observed to Ceriodaphnia dubia. The acute and chronic 

toxicity of other POTW effluents to C. dubia has also been attributed, in part, to diazinon 

(Amato et al. 1992; Bailey et al. 1997; Burkhard and Jensen 1993; Guinn et al. 1995). 

 Diazinon has also been detected in storm water runoff (non-point source) in urban and 

agricultural areas (Bailey et al. 1997, 2000; Domagalski et al. 1997; Kratzer 1999; McConnell et 

al. 1998; NCTCOG 1993; Waller et al. 1995). Domagalski et al. (1997) observed that in the 
3

western valley streams of the San Joaquin River, California, diazinon concentrations peaked 

within hours of a rainfall event and decreased thereafter. Diazinon was also detected in air 

samples over the Mississippi River from St. Paul to New Orleans, most likely related to use on 

cropland within 40 km of the river (Majewski et al. 1998). Rainfall runoff of pesticides with 

water solubility exceeding 10 mg/L, such as diazinon, can cause toxic additions to freshwater 

ecosystems (Wauchope 1978). A study by Ritter et al. (1974) showed that the highest 

concentration of diazinon measured in field runoff (82 μg/L), occurred after a storm event and 

corresponded to 0.1% of the total amount of diazinon applied to the experimental watershed. 

 The mobility of diazinon in soil is influenced by the organic matter (OM) and carbonate 

content of the soil (WHO 1998). Arienzo et al. (1994a,b) found that diazinon is slightly mobile 

in soils with a low or medium (< 2 percent) OM content and immobile in those with high OM 

content (> 2 percent). The sorption of diazinon to OM was enhanced when a sandy loam soil 

was modified with different exogenous organic materials containing humic-like substances 

relative to unmodified sandy loam soil (Iglesias-Jimenez et al. 1997). 

 Martinez-Toledo et al. (1993) found that the presence of 10 to 300 μg/g of diazinon in soil 

increased the total number of bacteria and the population of denitrifying bacteria. However, 

aerobic dinitrogen fixing bacteria numbers and dinitrogen fixation rate decreased initially (3 

days) at diazinon concentrations of 100 to 300 μg/g before recovering to control levels. 

Nitrifying bacteria and fungal soil populations were not affected by concentrations of 10 to 300 

μg/g diazinon in soil. 

 The fate of diazinon in the aquatic environment is thought to be regulated by two main 

processes - chemical hydrolysis and microbial degradation. Both processes are influenced by the 

conditions of pH, temperature and the organic content of the water. Diazinon is stable at pH 7.0 

and can persist in the environment for as long as six months. Ku et al. (1998b) found that 

cleavage of the phosphorous-oxygen bond was the critical step in the hydrolysis of diazinon. 

Diazinon half-life due to hydrolysis was 43.3 days in well water at pH 7.4 to 7.7 and 16oC 

(Morgan 1976) and 171 days at pH 7.3 and 21oC (Mansour et al. 1999). Diazinon, unlike other 

organophosphorus insecticides, hydrolyzes under both acidic and alkaline pH conditions (Gomaa 

et al. 1969). In the laboratory at 20oC the half-life was determined to be 12, 4436 and 146 hr at 

pH 3.1, 7.4 and 10.4, respectively (Faust and Gomaa 1972). Parkhurst et al. (1981) measured a 

degradation rate of two percent per day and a half-life of 39 days in diazinon treated river water 
4

at summer temperatures. The breakdown of diazinon in soils of flooded rice fields occurs at 

similar rates as in water and is described in a review by Sethunathan (1973). 

 A less dominant process influencing the fate of diazinon in aquatic systems is 

photodegradation. Scheunert et al. (1993) found that when diazinon solutions were irradiated 

with UV light of different wave lengths, photodegradation was greater in river or lake water than 

in distilled water. Medina et al. (1999) compared the half-life of diazinon in filtered Limon 

River samples under light and dark conditions and found that sunlight exposed samples had a 

shorter half-life (t1/2 = 31.13 days) than samples held in the dark (t1/2 = 37.19 days). 

 An important factor regulating the rate of microbial decomposition of diazinon is adaptation 

of microbes to the chemical. Microbes exposed repeatedly to diazinon had a markedly increased 

capacity to degrade diazinon compared to microbes exposed once to diazinon (Sethunathan and 

MacRae 1969; Sethunathan and Pathak 1972; Forrest et al. 1981). 

1.3. Toxicity of Diazinon 

 A primary mode of toxicity of organophosphorus insecticides is inhibition of 

cholinesterases present in the nervous system. Like most organophosphorous pesticides, 

oxidative desulfuration of diazinon to diazoxon results in greater anticholinesterase activity (Hill 

1995). Margot and Gysin (1957) have reported that the cholinesterase inhibiting activity of 

diazoxon is about 4,000 times greater than that of the parent diazinon. Diazoxon has been 

identified as a metabolite of diazinon in the liver microsomes of channel catfish, Ictalurus 

punctatus, and bluegill, Lepomis macrochirus (Hogan and Knowles 1972). Insect enzymes 

efficiently convert diazinon to the toxic oxygen homolog, diazoxon (Albert 1981). Crustacea 

very likely have similar ability to metabolize organophosphates. Insects and crustacea are 

generally more sensitive to organophosphorous insecticides than vertebrates, presumably due to 

less efficient detoxification of diazoxon by the invertebrates. 

 Diazinon, on prolonged storage, may become more toxic due to transformation products. 

Monosulfotepp was shown to be 14,000 times more potent than diazinon in a test of enzyme 

inhibition (Singmaster 1990). The use of an improperly stored diazinon formulation in which 

diazinon had transformed into the more toxic products sulfotepp and monothiono-tepp, was cited 

by Soliman et al. (1982) as the most probable cause of two acute human poisoning cases in 

Egypt. Sulfotepp has been reported to be 58 times more toxic to fathead minnows (Pimephales 
5

promelas), 75 times more toxic to bluegill (Lepomis macrochirus) and rainbow trout 

(Oncorhynchus mykiss), and 8.7 times more toxic to a cladoceran (Daphnia magna) than 

diazinon (Meier et al. 1979). The authors speculated that some of the toxicity attributed to 

diazinon is likely due to sulfotepp, which is no longer in commercial formulations of diazinon. 

1.4. Derivation of Aquatic Life Ambient Water Quality Criteria 

 A comprehension of the “Guidelines for Deriving Numerical National Water Quality 

Criteria for the Protection of Aquatic Organisms and Their Uses” (Stephan et al. 1985), hereafter 

referred to as the Guidelines, is necessary to fully understand the text, tables, and calculations 

presented in this criteria document. Results of intermediate calculations are presented to four 

significant figures to prevent round-off error in subsequent calculations, not to reflect the 

precision of the value. Final criteria values are presented to two significant figures. 

 The latest comprehensive literature search for information used in developing this document 

was conducted in November 1999. An additional literature search, limited to identifying 

information regarding diazinon effects on olfaction, was conducted in 2004. Data in the files of 

the U.S. EPA’s Office of Pesticide Programs concerning the effects of diazinon on aquatic 

organisms have also been evaluated in deriving the aquatic life criteria for diazinon. 

 Whenever adequately justified, a national criterion may be replaced by a site-specific 

criterion (U.S. EPA 1983), which may include not only site-specific criterion concentrations 

(U.S. EPA 1994), but also site-specific averaging periods and frequencies of allowed excursions 

(U.S. EPA 1991). 
6

2. ACUTE TOXICITY TO AQUATIC ANIMALS 

2.1. Freshwater 

 The acute toxicity of diazinon to freshwater animals has been determined for 13 

invertebrate species, 10 fish species and one amphibian species (Table 1). Acute toxicity values 

ranged from 0.25 μg/L for the cladoceran, Ceriodaphnia dubia (Norberg-King 1987), to 11,640 

μg/L for planaria, Dugesia tigrina (Phipps 1988). The most sensitive organisms tested were 

invertebrates in the Class Crustacea. The cladoceran, C. dubia, had the lowest Genus Mean 

Acute Value (GMAV) which was calculated from 14 tests (0.3773 μg/L; Table 3), ten of which 

were conducted by the U.S. EPA’s Office of Research and Development (Norberg-King 1987; 

Ankley et al. 1991). Results from these 14 tests were relatively consistent (acute values ranged 

from 0.25 to 0.59 μg/L) considering that different water sources were used and organism age at 

test initiation ranged from < 6 hr-old to < 48 hr-old. C. dubia data were included in Table 1 

when the organisms received food during the exposure, but these data were not used to calculate 

the Species Mean Acute Value (SMAV), as per the Guidelines (Stephan et al. 1985). Three 

other cladoceran species (Daphnia pulex, Daphnia magna, and Simocephalus serrulatus) were 

tested and their sensitivity to diazinon found to be similar to that of C. dubia with EC50s ranging 

from 0.65 to 1.8 μg/L. The toxicity of diazinon to three species of amphipods (Gammarus 

faciatus, Gammarus pseudolimneaus, and Hyallela azteca) was tested, and the 96-hr LC50s 

ranged from 2.04 to 16.82 μg/L. Toxicity test data were available for two insect species. LC50s 

of 10.7 μg/L for the midge, Chironomus tentans, and 25 μg/L for the stonefly, Pteronarcys 

californica, were reported. These data show that insect sensitivity to diazinon toxicity is in the 

same range as amphipods. 

 The least sensitive species tested with diazinon was also an invertebrate. The planarian, 

Dugesia tigrina, had the highest observed diazinon 96-hr LC50 of 11,640 μg/L. Other 

invertebrate species exhibiting relatively low sensitivity to diazinon included the snail, Gillia 

altilis (96-hr LC50 of 11,000 μg/L), the oligochaete worm, Lumbriculus variegatus (individual 

test 96-hr LC50 values of 9,980 and 6,160 μg/L, and SMAV of 7,841 μg/L) and the apple snail, 

Pomacea paludosa (individual test 96-hr LC50 values of 2,950, 3,270 and 3,390 μg/L and 

SMAV of 3,198 μg/L). 

 The only amphibian toxicity test available was for the green frog, Rana clamitans. The frog 
7

embryos were exposed to three concentrations of diazinon (0.5, 5.0 and 50 μg/L). The 96-hr 

LC50 was reported as > 50 μg/L (Harris et al. 1998). 

 Freshwater fish species that were tested showed moderate sensitivity to diazinon. SMAVs 

ranged from 425.8 μg/L for the rainbow trout, Oncorhynchus mykiss, to 9,000 μg/L for the 

goldfish, Carassius auratus (Table 1). Diazinon toxicity to rainbow trout was evaluated in five 

tests with LC50 values ranging from 90 μg/L (Cope 1965b; Ciba-Geigy 1976; Johnson and 

Finley 1980; Mayer and Ellersieck 1986) to 3,200 μg/L (Bathe et al. 1975a). The cutthroat trout, 

Oncorhynchus clarki, was generally less sensitive (SMAV = 2,166 μg/L) to diazinon than 

rainbow trout (SMAV = 425.8 μg/L). Certain species of warmwater fish, flagfish (Jordanella 

floridae), fathead minnow (Pimephales promelas), goldfish (Carassius auratus), and zebrafish 

(Danio rerio; formerly Brachydanio rerio) are less sensitive to diazinon than the coldwater 

species, rainbow trout, brook trout (Salvelinus fontinalis), and lake trout (Salvelinus namaycush). 

Two exceptions include the warmwater bluegill, which is more sensitive to diazinon than the 

coldwater fish species, and the coldwater cutthroat trout, which is less sensitive than the 

warmwater flagfish. For the four most sensitive genera, all crustaceans, the GMAVs differed by 

a factor of 15.5 (Table 3 and Figure 1). Based on available data for freshwater organisms, as 

summarized in Table 1, the freshwater Final Acute Value (FAV) is 0.3397 μg/L. 

2.2. Saltwater

 The acute toxicity of diazinon to saltwater animals has been determined for 7 invertebrate 

species and 2 fish species (Table 1). SMAVs ranged from 2.57 μg/L for the copepod, Acartia 

tonsa (Khattat and Farley 1976), to > 9,600 μg/L for embryos of the sea urchin, Arbacia 

punctulata (Thursby and Berry 1988), which is a difference among species of >3,735-fold. 

Acute values for the mysid, Americamysis bahia (formerly Mysidopsis bahia), determined from a 

renewal, unmeasured test (8.5 μg/L) were approximately two-fold higher than those determined 

from a flow-through measured test (4.82 μg/L). Acute toxicity test data available for other 

saltwater invertebrates include an annelid worm (Neanthes arenaceodentata), an amphipod 

(Ampelisca abdita), and two species of shrimp, grass shrimp (Palaemonetes pugio) and pink 

shrimp (Penaeus duorarum) (Table 1). The saltwater fish, inland silverside (Menidia beryllina), 

was relatively insensitive to diazinon with a LC50 of 1,170 μg/L. The remaining fish species, 

the sheepshead minnow (Cyprinodon variegatus), had an LC50 value of 1,400 μg diazinon/L, 
8

and is the only saltwater fish with a corresponding chronic value. Acute values for the four most 

sensitive genera, all invertebrates, differed by only a factor of 2.6 (Table 3 and Figure 2). Based 

on available data for saltwater organisms, as summarized in Table 1, the saltwater Final Acute 

Value (FAV) is 1.637 μg/L. 
9

3. CHRONIC TOXICITY TO AQUATIC ANIMALS

3.1. Freshwater 

 The chronic toxicity of diazinon was determined for 4 freshwater species, 3 fish and 1 

invertebrate (Table 2). A life-cycle test consisting of a 7-day exposure period was conducted 

with C. dubia (Norberg-King 1987). Diluted mineral reconstituted water was used to culture and 

expose the organisms. All organisms survived in the control and the three lowest diazinon 

exposures (0.063, 0.109, and 0.220 μg/L). There also was no effect on reproduction in the three 

lowest diazinon exposures. No organisms survived at diazinon concentrations > 0.520 μg/L. 

The chronic value for C. dubia was 0.3382 μg/L. Dividing the acute value derived from ten 48-

hr acute tests (0.3760 μg/L; Table 1) conducted in the same laboratory with the same dilution 

water (Norberg-King 1987; Ankley et al. 1991) by the chronic value (0.3382 μg/L; Table 2) 

results in an Acute-Chronic Ratio (ACR) of 1.112 for C. dubia (Table 2). 

 Allison and Hermanutz (1977) conducted a partial life-cycle test with brook trout, 

Salvelinus fontinalis. The test began with yearlings, which were exposed for 173 days to 

measured concentrations ranging from 0.55 to 9.6 μg/L. Each replicate was thinned to two males 

and four females, and exposure continued during spawning for an additional two months, during 

which time eggs were collected and viability (% hatch) determined. Larvae were thinned to 25 

per chamber and exposure continued for 122 additional days. Average measured concentrations 

during egg viability and larval growth periods ranged from 0.8 to 11.1 μg/L. After 173 days, 

survival of parental stock was significantly reduced at 9.6 μg/L, but not at 4.8 μg/L. However, 

some deformities were seen and the instantaneous growth rate was reduced by 4.8 μg/L diazinon. 

The authors state that high within-treatment variance in egg viability prevented any accurate 

analysis of egg production, egg viability or hatch, but there were viable eggs produced at every 

concentration. Brook trout progeny from the 122 day larval exposure showed some measurable 

effects after 30 days. At 122 days post-hatch, fish in all exposure concentrations had average 

weights significantly less than the control fish. The chronic value for this species is < 0.8 μg/L, 

which is the lowest exposure concentration for the progeny in which growth effects were 

observed. Dividing the acute value (723.0 μg/L; Table 1) calculated from three 96-hr acute tests 

(Allison and Hermanutz 1977) by the chronic value (< 0.8 μg/L; Table 2) results in an ACR of > 

903.8 for brook trout (Table 2). 
10

 Norberg-King (1989) exposed fathead minnow embryos and the resulting larvae to diazinon 

for 32 days in an early-life stage test. At test termination, wet weight and survival of fish 

exposed to only the highest exposure concentration (285 μg/L) were significantly different from 

that of the control fish. Total length was significantly affected at concentrations > 60 μg/L and 

dry weight was significantly reduced at 37.8 μg/L, but not at 16.5 μg/L. Based on reduced dry 

weight, the chronic value for the test was 24.97 μg/L. Dividing the acute value (9,350 μg/L; 

Table 1), determined by another group of researchers (University of Wisconsin-Superior 1988) at 

the same laboratory using the same water supply and the same genetic stock of fish, by the 

chronic value (24.97 μg/L; Table 2) results in an ACR of 374.4 for fathead minnow (Table 2). 

 In another test, fathead minnow embryos (< 24-hr old) and the resulting larvae were 

exposed to diazinon for a total of 32 days (Jarvinen and Tanner 1982). Results of the early-life 

stage test were reduced survival at diazinon concentrations > 290 μg/L and reduced weight 

(10.1% reduction) at 90 μg/L, but no weight difference from the control fish at 50 μg/L. Based 

on reduced weight, the chronic value for the test was 67.08 μg/L. Dividing the acute value 

(6,900 μg/L), determined from a flow-through test in which toxicant concentration was measured 

(Jarvinen and Tanner 1982; Table 1), by the chronic value (67.08 μg/L; Table 2) results in an 

ACR of 102.9 for fathead minnow. Calculating the geometric mean of the two ACRs for fathead 

minnow (374.4 and 102.9) results in a species mean acute-chronic ratio (SMACR) of 196.3 for 

the fathead minnow (Table 2). 

 The flagfish, Jordanella floridae, was expsosed to diazinon in a life-cycle test (Allison 

1977). The study began with one-day-old larvae and continued through spawning, which 

occurred at about 60 days, and then continued with the fish progeny for 35 days post-hatch. The 

only significant effect on the parental stock was a reduction (23.3%) in the average wet weight of 

the male fish after 61 days of exposure to 88 μg/L diazinon. This effect is based on only two fish 

per replicate because the fish were culled to two males and five females per treatment (from 30 

fish per treatment at start of test) prior to spawning. Weight of the female fish was not 

significantly different from controls at any exposure concentration although there was a 21.4% 

reduction in the average weight of female fish exposed to 88 μg/L diazinon. There was a 

significant reduction in percent hatch at diazinon concentrations of 88 μg/L. Average weight at 

35 days post-hatch was significantly reduced in the two lower diazinon exposure groups (14 and 

26 μg/L), but not in the two higher diazinon exposure groups (54 and 88 μg/L), hence, a dose-
11

dependent effect on this endpoint was not observed. The chronic value for flagfish, based on 

hatch success, is the geometric mean of 54 μg/L (NOEC) and 88 μg/L (LOEC), or 68.93 μg/L. 

Dividing the acute value (1,643 μg/L; Table 1), which is the geometric mean of results from two 

tests conducted in the same water supply and using fish from the same culture as used in the 

chronic test (Allison and Hermanutz 1977), by the chronic value (68.93 μg/L; Table 2) results in 

an ACR of 23.84 for the flagfish (Table 2). 

3.2. Saltwater 

 The chronic toxicity of diazinon to saltwater organisms has been determined in a life-cycle 

test with the mysid, A. bahia, and a partial life-cycle test with the sheepshead minnow (Table 2). 

The mysid test (Nimmo et al. 1981) was of 22 days duration, and the authors’ original data was 

used to recalculate the chronic limits (Berry 1989). There was no statistical difference in 

survival observed at any of the concentrations tested (0.54, 1.2, 2.1, 4.4 μg/L). The number of 

young per female was not significantly reduced relative to controls at diazinon concentrations <

2.1 μg/L. There were no young produced by females exposed to the highest concentration tested 

(4.4 μg/L). Based on reproduction, the chronic value for the mysid is the geometric mean of the 

chronic limits, 2.1 and 4.4 μg/L, or 3.040 μg/L. Dividing the acute value (4.82 μg/L; Table 1), 

determined by the same authors (Nimmo et al. 1981), by the chronic value (3.040 μg/L) results in 

an ACR of 1.586 for the mysid, A. bahia (Table 2). 

 Sheepshead minnow, Cyprinodon variegates, reproduction was significantly reduced in all 

diazinon exposure concentrations during a partial life-cycle test (Goodman et al. 1979). The 

number of eggs spawned per female in the 0.47, 0.98, 1.8, 3.5 and 6.5 μg/L (average measured) 

diazinon concentrations were 69, 50, 50, 55 and 45 percent of control fish, respectively. Neither 

survival nor growth was affected by diazinon exposures < 6.5 μg/L. Based on reduction of eggs 

spawned, the chronic value for sheepshead minnow is < 0.47 μg/L (Table 2). Dividing the acute 

value (1,400 μg/L; Table 1) determined by the same authors (Goodman et al. 1979) by the 

chronic value (< 0.47 μg/L) results in an ACR of > 2,979 for sheepshead minnow. 

3.3. Acute-Chronic Ratios 

 Chronic toxicity tests have been conducted on six aquatic species and chronic values ranged 

from 0.3882 μg/L for Ceriodaphnia, C. dubia, to 68.93 μg/L for flagfish (Table 2). The chronic 
12

values for brook trout (< 0.8 μg/L) and sheepshead minnow (< 0.47 μg/L) cannot be determined 

accurately because all concentrations tested affected reproduction and growth. Acute-chronic 

ratios for acutely sensitive crustacean invertebrates were 1.586 for mysids and 1.112 for C. dubia

(Table 2). In contrast, ratios are markedly higher for relatively acutely insensitive fishes: 23.84 

for flagfish, 102.9 and 374.4 for fathead minnow (Pimephales promelas), > 903.8 for brook trout 

(Salvelinus fontinalis), and > 2,979 for sheepshead minnow. 

 The Guidelines (Stephan et al. 1985) specify that if the species mean acute-chronic ratio 

(SMACR) seems to increase or decrease as the SMAV increases, the Final Acute-Chronic Ratio 

(FACR) should be calculated as the geometric mean of the ACRs for species whose SMAVs are 

close to the FAV. It does appear that ACR values are lower for species acutely sensitive to 

diazinon and higher for acutely insensitive species (Table 3). Therefore, only the acutely 

sensitive C. dubia and A. bahia ACRs were used to calculate the FACR of 1.328. The 

Guidelines also stipulate that if the most appropriate SMACRs are less than 2.0, acclimation has 

probably occurred during the chronic test and the FACR should be assumed to be 2.0. The low 

ACRs for C. dubia and A. bahia support the finding that diazinon toxicity is rapid for these 

sensitive invertebrates and extended periods of exposure do not increase toxicity for these 

sensitive species. Thus, the FACR for diazinon is 2.0. The Final Chronic Values (FCV) for 

freshwater and saltwater are 0.1699 and 0.8185 μg/L, respectively (FAVs divided by 2.0). Use 

of an FACR of 2.0 results in the same value for the Criteria Maximum Concentration (CMC; 

acute criterion) and the Criteria Continuous Concentration (CCC; chronic criterion). 

 It appears from available data that the freshwater Final Chronic Value will protect the tested 

freshwater species against adverse effects due to diazinon (Figure 3). Growth of offspring of 

exposed brook trout, a recreationally important freshwater fish species, was statistically 

significantly reduced by 40% at the lowest tested concentration of 0.8 μg/L, which is a factor of 

4.7 times the CCC. However, the chronic value for this study is a less than value and it is 

uncertain how close to the freshwater CCC adverse effects may occur. Reproduction of the 

saltwater sheepshead minnow was statistically significantly reduced by 31% at the lowest tested 

concentration of 0.47 μg/L, which is below the saltwater CCC. Therefore, where exposure to 

diazinon at or near CCC levels may occur to this or similar saltwater fish species, states and 

tribes may want to consider site-specific criteria derivations for diazinon. 
13

4. TOXICITY TO AQUATIC PLANTS 

 Acceptable data on the effects of diazinon to freshwater algae (nonvascular plant) are 

available for one species (Table 4), but no acceptable data are available regarding the toxicity to 

freshwater vascular plants. Hughes (1988) exposed the green alga, Selenastrum capricornutum, 

for seven days in a static test. A 7-day EC50 of 6,400 μg/L (measured concentration) was 

determined based on reduced cell numbers. No saltwater tests with plants are suitable, according 

to the Guidelines, for inclusion in this section. Some additional freshwater and saltwater plant 

toxicity information is included with “Other Data.” Based on a single aquatic plant test, the 

Final Plant Value for diazinon is 6,400 μg/L. 
14

5. BIOACCUMULATION 

 Three freshwater species of fish, rainbow trout (Oncorhynchus mykiss), carp (Cyprinus 

carpio) and guppy (Poecilia reticulata), were exposed to diazinon for 14 days and the whole 

body tissue concentrations were determined (Seguchi and Asaka 1981; Keizer et al. 1993). 

Diazinon accumulated rapidly in the fish and reached steady-state in approximately three days. 

The bioconcentration factor (BCF) for rainbow trout and carp exposed to 15 μg diazinon/L was 

62 and 120, respectively (Table 5). The half-life for diazinon in these fish was less than seven 

days. The BCF for guppy exposed to 350 μg diazinon/L was 188 (Keizer et al. 1993). 

 In a 108-day saltwater exposure, uptake of diazinon by the sheepshead minnow was rapid, 

reaching steady state within 4 days (Goodman, et al. 1979). Whole body (less brain) 

bioconcentration factors for fish exposed to 1.8, 3.5 and 6.5 μg/L were 147, 147 and 213, 

respectively (Table 5). 
15

6. OTHER DATA 

6.1. Freshwater

 Additional data on lethal and sublethal effects of diazinon on freshwater species are 

presented in Table 6. Sewage microbes (Bauer et al. 1981) and actinomycete bacteria 

(Sethunathan and MacRae 1969) appear to be unaffected or have growth enhancement at 

diazinon concentrations near water saturation. 

 Sensitivity to diazinon varies greatly among green plants and diatoms tested. The green 

algal (non-vascular plant) species, Chlorella ellipsoidea and Chlamydomonas sp., were affected 

only at concentrations of 100,000 μg/L. The green algae Scenedesmus quadricauda was not 

affected at 1,000 μg/L (Stadnyk and Campbell 1971), but a mixture of green alga and diatoms 

had reduced growth at < 10 μg/L (Butler et al. 1975a). Exposure of the vascular plant, duckweed 

(Wolffia papulifera), to diazinon for 11 days resulted in 100 percent mortality at 100,000 μg/L 

saturation and deformities at 10,000 μg/L (Worthley and Schott 1971). 

 Various species of protozoans and invertebrates have been tested and found to have 

relatively low sensitivity to diazinon compared to crustacean and vertebrate species. Adverse 

affects were reported for protozoans at approximately 3,000 μg/L (Evtugyn et al. 1997). The 

rotifer, Brachionus calyciflorus, was found to be substantially less sensitive than cladocerans and 

insects to diazinon with respect to survival (24-hr LC50 = 29,220 μg/L), filtration and ingestion 

rates (50 percent reduction at 14,000 μg/L), reproduction (decreased reproduction at < 5,000 

μg/L), and median time to lethal effects (LT50 values ranged from 2.5 to 4 days for 14,000 and 

5,000 μg/L, respectively) (Fernandez-Casalderrey 1992a,b,c,d). Juchelka and Snell (1994) 

estimated a 48-hr no effect concentration (NOEC) for ingestion rate of 20,000 μg/L and Snell 

and Moffat (1992) calculated a NOEC for reproduction of 8,000 μg/L for B. calyciflorus. 

Chatterjee and Konar (1984) determined a 96-hr LC50 of 2,220 μg/L for the tubificid worm, 

Branchiura sowerbyi. Rogge and Drewes (1993) determined that 20,000 μg/L diazinon was 

lethal to the oligocheate worm, Lumbriculis variegatus, in 4 hours. A snail species (Physa 

acuta) had a 48-hr LC50 of 4,800 μg/L (Hashimoto and Nishiuchi 1981) which is near the upper 

end of the range of fish 96-hr LC50s. 

 Dortland (1980) conducted a series of tests with the cladoceran, Daphnia magna, and found 

in one exposure that 0.2 μg/L did not affect the organisms during the 21-day exposure, but 0.3 
16

μg/L reduced reproduction and mobility. In four other 21-day tests in which the D. magna were 

fed, EC50s ranged from 0.22 to 0.8 μg/L. In 21-day renewal tests with D. magna, FernandezCasalderrey et al. (1995) determined survival NOEC and LOEC of 0.15 μg/L and 0.18 μg 

diazinon/L (unmeasured concentrations), respectively. The mean total young per female (which 

was slightly less than that required by the ASTM test method) and mean brood size were both 

significantly reduced at the lowest exposure concentration (0.15 μg/L) when compared to the 

controls. A 24-hr LC50 of 0.86 μg/L for D. magna (unfed during test) was reported by the same 

authors. Sanchez et al. (1998, 1999 and 2000) reported chronic effects of diazinon to D. magna

in a series of tests to evaluate the toxicity of this pesticide over several generations. Test 

solutions (which were reported mistakenly as ng/L instead of μg/L), were measured initially, but 

not thereafter during each test. Although test solutions were renewed daily, dissolved oxygen 

concentrations were not reported. The lowest test concentration (0.05 μg/L) significantly 

reduced survival, growth and the number of young per female of the parental generation (F0) 

(Sanchez et al. 1998). The progeny (first and third broods), which were transferred to clean 

water in separate 21-day tests (Sanchez et al. 1999), showed similar responses to that of control 

animals, indicating that diazinon was being eliminated after parental exposure. However, 

adverse effects to progeny (first and third broods) that were continually exposed to the same test 

solutions as the parental generation for an additional 21-days were observed at the lowest tested 

concentration (0.05 μg/L) (Sanchez et al. 2000). A test in which D. magna were exposed to an 

insecticidal soap formulation of diazinon yielded similar results with a 48-hr LC50 of 0.74 μg/L 

and a 96-hr LC50 of 0.21 μg/L (Nishiuchi and Hashimoto 1967 and Hashimoto and Nishiuchi 

1981).

 Amphipods are generally very sensitive to diazinon toxicity. Collyard et al. (1994) 

compared the sensitivity of different H. azteca age groups to diazinon. The eight different age 

groups (0-2 to 24-26 days old at test initiation) had very similar 96-hr LC50 values that ranged 

from 3.8 to 6.2 μg/L. Werner and Nagel (1997) tested adult Hyallela azteca and reported an 

LC50 of 19 μg/L for this life stage. 

 Mosquito larvae appear to be about as sensitive to diazinon as cladocerans and amphipods. 

Yasuno and Kerdpibule (1967) exposed mosquito larvae (4th instar), Culex pipiens fatigans, to 

diazinon for 24 hr and measured LC50s ranging from 1.8 to 5.7 μg/L. Chen et al (1971) reported 

24-hr LC50s of 61-350 μg/L for younger life stages (3rd-4th instar) of the same species. Klassen 
17

et al (1965) found the mosquito species, A. eqyptii, to be less sensitive (24-hr LC50 = 350 μg/L) 

than Culex pipiens fatigans. Caddisfly larvae exposed to diazinon for 6 hr had highly variable 

LC50s, ranging from 500 to 2,500 μg/L for Hydropsyche morosa and > 500 μ/L for H. recurvata

(Fredeen 1972). The EC50 for a species of stonefly, Pteronarcys californicus, exposed to 

diazinon for 48 hr was reported as 74 μg/L (Cope 1965a). 

 Rainbow trout fingerlings were exposed to diazinon concentration of 8, 40 and 200 μg/L 

(unmeasured) under flow-through conditions for 28 days (Bresch 1991). Survival and growth of 

rainbow trout in the three treatment groups after 28 days were not statistically (p > 0.05) 

different from the control group. The chronic value for rainbow trout in this test was > 200 μg/L 

diazinon. Rainbow trout were also exposed to an insecticidal soap formulation of diazinon for 

96 hr (Mitchell 1985) and an unspecified form of diazinon for 48 hr (Cope et al 1965a), and the 

LC50s determined were 20 μg/L and 170 μg/L, respectively. Cutthroat trout of two sizes were 

exposed to an unspecified formulation of diazinon for 96 hr and LC50s of 3,850 μg/L for the 

smaller fish and 2,760 μg/L for the larger fish determined (Swedberg 1973). The LC50s for 

rainbow trout and cuttthroat trout were consistent with the values used in Table 1 for the same 

species. Brown trout, Salmo trutta lacustris, were also relatively sensitive to diazinon having a 

96-hr LC50 value of 602 μg/L for an unspecified formulation of diazinon (Swedberg 1973). 

 Carp and goldfish are relatively tolerant of diazinon in acute exposures with 48-72 hr LC50s 

ranging from 1420 μg/L (carp) to 5100 (goldfish) μg/L (Table 6). Diazinon (technical grade) 

was toxic to newly hatched fathead minnow larvae at seven- and twelve-days exposure (Table 6), 

but the sensitivity increased as the exposure was continued to 32-days (Table 1) (Norberg-King 

1989). The more sensitive timepoint was used in calculating the criteria. 

 Jarvinen and Tanner (1982) exposed fathead minnows to an encapsulated formulation of 

diazinon in acute and chronic exposures. The encapsulated formulation was less acutely toxic 

(5,100 and 6,100 μg/L; Table 6) than the technical grade (2,100 and 4,300 μg/L; Table 1) 

following 96-hr exposures. Exposure of embryo-larval stage fathead minnows for 32 days to the 

encapsulated formulation resulted in a chronic value of 55.14 μg/L. Dividing the acute value by 

the chronic value results in an ACR for the encapsulated formulation of 101.6, which is 

comparable to the ACR of 102.9 for the technical grade chemical (Table 2). Ciba-Geigy (1976) 

reported 96-hr LC50s of 8,000 μg/L and 150 μg/L for catfish (Ictalurus sp.) and Ide (Leucisuc 

idus) respectively, exposed to diazinon as an emulsifiable concentrate (60%). 
18

 Flagfish, J. floridae, have been exposed in a 21-day pulsed dose exposure with diazinon 

followed by a period without the chemical to observe effects (Allison 1977). Exposure of the 

parental stock beginning at hatch and lasting 21 days resulted in decreased egg production by the 

females at concentrations > 290 μg/L. Exposure to diazinon for 21 days just prior to spawning 

resulted in decreased parental survival at concentrations > 250 μg/L, but there were no effects on 

reproduction at the 250 and 450 μg/L exposure concentrations. Exposure of adults to diazinon 

for 21 days once spawning had initiated resulted in decreased survival of the parents at the 

highest exposure concentration (1,170 μg/L) and reduced survival of larval progeny at 1,170 

μg/L. 

 Chen et al. (1971) exposed the guppy, P. reticulata, to diazinon and measured 24-hr LC50s 

of 3,700 and 3,800 μg/L. These values were in agreement with the work of Ciba-Geigy (1976) 

which measured a 96-hr LC50 of 3,000 μg/L for the same fish species. Ohayo-Mitoko and 

Deneer (1993) estimated a lethal body burden of 2,495 μg diazinon/L for the guppy. Relative to 

some other fish species, the guppy appears to be more tolerant of diazinon than trout species but 

less tolerant than tested cyprinid species (fathead minnow and goldfish). 

 Bluegill, L. macrochirus, was tested by two research groups with widely different results 

(Table 6). The results of Cope (1965a) indicate that the bluegill is a relatively sensitive species 

(48-hr EC50 = 30 μg/L), whereas the work of Li and Chen (1981) indicate intermediate 

sensitivity (48-hr LC50 = 1,493 μg/L) relative to other fish species. 

 Bresch (1991) evaluated the toxicity of diazinon to zebrafish in an early life-stage test. 

Zebrafish were exposed to diazinon from egg stage (approximately 2-3 hr after spawning) 

through juvenile stage to diazinon concentrations of 8, 40 and 200 μ g/L (unmeasured) for 42 

days under flow-through conditions. Survival and growth in the three treatment groups were not 

statistically different (p > 0.05) from the controls. Thus, the zebrafish chronic value was > 200 

μg/L. 

 Bioconcentration factors were determined for various aquatic species with a value of 4.9 for 

the crayfish, Procambarus clarkii (Kanazawa 1978), 17.5 for the guppy (Kanazawa 1978), 28 for 

oriental weatherfish, Misgurnus anguillicaudatus (Seguchi and Asaka 1981), 62 for rainbow 

trout (Seguchi and Asaka 1981), and for carp 20.9 (Tsuda et al. 1990), 65.1 (Kanazawa 1978) 

and 120 (Seguchi and Asaka 1981). 

 Outdoor experimental channels at EPA’s Monitcello Ecological Research Station 
19

(Mississippi River water) were used by Arthur et al. (1983) to evaluate the effects of diazinon on 

macroinvertebrates. One channel served as a control and two other channels as low and high 

treatments. The low and high treatment channels were continuously treated to achieve either 0.3 

or 3 μg/L nominal diazinon concentrations for 12 weeks, then increased to 6 and 12 μg/L 

nominal diazinon concentrations for four weeks, and finally the high treatment channel was 

increased to 30 μg/L and the low treatment channel allowed to returned to ambient conditions. 

Only the first 12 week dosing regime achieved nominal diazinon levels as indicated by analytical 

measurements. During the latter two dosing regimes the channel water did not reach the 

intended concentrations. No consistent interchannel differences were observed in total 

macroinvertebrate abundance or in species diversity indices. Hyalella was the most sensitive 

species in the test, exhibiting substantially higher (5 to 8 times) drift rates in the 0.3 μg/L 

diazinon treated channel relative to the control channel, and had sharply reduced population 

levels at diazinon concentrations of 5 μg/L. Macroinvertebrate tolerance to diazinon treatment 

was observed as: flatworms, physid snails, isopods and chironomids (most tolerant); leeches and 

the amphipod Crangonyx (less tolerant); the amphipod Hyalella, mayflies, caddisflies and 

damselflies (least tolerant). 

 An aquatic pulsed exposure microcosm study was conducted with technical grade diazinon 

by Giddings et al. (1996). The objectives of the study were to measure the effects of a range of 

diazinon exposure regimes to many taxonomic groups under simulated field conditions and to 

determine the relationship between the level of diazinon exposure and the magnitude of 

ecological response. Eighteen fiberglass tanks, each 3.2 m in diameter and 1.5 m in depth, were 

established with sediment and water (11.2 m3

) from natural ponds and stocked with 40 juvenile 

bluegill sunfish (L. macrochirus). Diazinon was applied in aqueous solution three times at 7-day 

intervals. Eight loading rates were used, with two microcosms at each load rate plus two 

controls. The amount of diazinon added during each application corresponded to nominal 

concentrations ranging from 2.0 μg/L to 500 μg/L. The most sensitive ecological components of 

the microcosms were zooplankton (Cladocera) and chironomid insects (Pentaneurini and 

Ceratopogonidae), which were reduced at all treatment levels. Effects on many zooplankton and 

macroinvertebrate taxa occurred at diazinon concentrations (time-weighted averages) of 9.2 μg/L 

and higher. Total fish biomass was reduced at 22 μg/L and higher, and fish survival was reduced 

at 54 μg/L and higher. Odonates, some dipterans, and plants were not adversely affected by 
20

diazinon at 443 μg/L, the highest concentration tested. Microcosm results were consistent with 

laboratory toxicity data for some taxa (e.g., cladocerans, Ephemeroptera, and bluegill sunfish), 

but differed substantially for others (e.g., rotifers, Chironomini, and odonates). The NOEC for 

the microcosms study (70-d time-weighted average) was reported as 4.3 μg/L. 

6.2. Saltwater 

 Other data on the lethal and sublethal effects of diazinon on saltwater species (Table 6) did 

not indicate greater sensitivities than data represented in Tables 1 and 2. Saltwater algae appear 

to be less sensitive to diazinon than most aquatic animals. Photosynthesis of natural 

phytoplankton was essentially unaffected by a 4-hr exposure to 1,000 μg/L diazinon (Butler 

1963). There was no effect of diazinon at 1,000 μg/L on sexual reproduction of the red alga, 

Champia parvula (Thursby and Tagliabue 1988). A 24-hr exposure of the red alga, Chondrus 

crispus, to 10,000 μg/L diazinon had no effect on the growth of the alga in a subsequent 18-day 

grow-out period (Shacklock and Croft 1981). Rotifers, Brachionis plicatilis, were also not 

acutely sensitive to diazinon (Thursby and Berry 1988; Guzzella et al 1997). No effect on 

growth of eastern oysters, Crassostrea virginica, was observed following a 96-hr exposure to 

1,000 μg/L diazinon (Butler 1963), however, an LC50 of 1,115 μg/L was reported by Williams 

(1989). Shacklock and Croft (1981) reported that two days after a 3-hr exposure to 1,000 μg/L 

diazinon, mortality of the saltwater snail, Lacuna vincta, test organisms was 88% whereas 

mortality of the amphipod, Gammarus oceanicus, and the isopod, Idotea baltica, was 100%. 

Longer exposure (48-hr) of the adult amphipods, Ampelisca aldita and Rheopoxynius abronius, 

resulted in LC50 values of 10 and 9.2 μg/L, respectively. The brown shrimp, Penaeus aztecus, 

had a 24-hr EC50 of 44 μg/L (Butler 1963) and a 48-hr EC50 of 28 μg/L (Mayer 1987). 

Similarly, an acute (48-hr) EC50 of 28 μg/L has been reported for for grass shrimp, 

Palaemonetes pugio (Mayer 1987). The 24- and 48-hr LC50s for the white mullet, Mugil 

curema, were both 250 μg/L (Butler 1963) and the 48-hr LC50 for striped mullet, Mugil 

cephalus, was 150 μg/L (Mayer 1987). In the partial life-cycle test conducted with sheepshead 

minnow by Goodman et al. (1979), acetylcholinesterase activity in fish exposed to 0.47 μg/L 

diazinon were consistently less than control fish activity and averaged 71% inhibition in the fish 

exposed to 6.5 μg/L diazinon. A BCF of 56 was reported for Eastern oyster exposed to diazinon 

for 5 days (Williams 1989). 
21

6.3. Olfactory Effects of Diazinon in Aquatic Organisms 

 Olfaction (the sense of smell) is important to aquatic organisms, especially fish, because 

feeding, defense, schooling, spawning and migration are significantly influenced by olfactory 

cues (Hara et al. 1976). A well known example of the importance of olfaction in aquatic 

organisms is the ability of salmon and other migratory fish to follow scents in the water to find 

natal streams after an extended stay in the distant ocean. 

 Several studies have been conducted to explore whether certain chemicals may alter 

detection of olfactory cues by damaging organelles, interacting with membrane receptor sites, or 

masking biologically important chemical signals. A laboratory technique for measuring 

peripheral olfactory function in fish is the use of electric field potential recordings (Baatrup et al. 

1990, Winberg et al. 1992). The amplitude of the EOG reflects the summed electrical response 

of olfactory receptor neurons as they bind to molecules in the surrounding environment. Shortterm exposure of the olfactory epithelium of mature male Atlantic salmon (Salmo salar) parr to >

1.0 μg/L of diazinon reduced the olfactory electrophysiological response to pheromonallymediated endocrine system (prostaglandin F2α) as measured by their olfactory epithelium EOG 

electrical response (Moore and Waring 1996, 1998; Moore and Lower 2001). 

 The majority of studies associated with olfactory effects do not report effects on olfactory 

organs or physiology directly, but rather evaluate the effects of chemicals on the behavior of fish 

that are associated with olfactory cures, including preference/avoidance reactions, feeding and 

swimming responses. Chu and Lau (1994) studied the effect of diazinon on the behavioral 

response of the shrimp Metapenaeus ensis to a known amino acid attractant. They found that 

exposure to 0.1 μg/L diazinon significantly reduced the shrimp’s ability to find and grasp the 

food source. Scholz et al. (2000) found that the diazinon significantly disrupts olfactorymediated anti-predator responses and homing behavior of chinook salmon (Oncorhynchus 

tshawytscha) at 1.0 and 10.0 μg/L, respectively. Swimming behavior and visually guided food 

capture were not affected at diazinon concentrations as high as 10.0 μg/L. 

 In several other laboratory studies, researchers have attempted to link affects on 

biochemical and physiological responses (e.g., receptor cell loss, neuron degeneration or 

depressed EOG/neurotransmission) with abnormal fish behavior including disruption of 

preference/avoidance reactions, depressed feeding and erratic swimming (Beyers and Farmer 
22

2001; Hansen et al. 1999; Saglio et al. 2001). Beauvais et al. (2000) exposed larval rainbow 

trout (Oncorhynchus mykiss) for 96 hours to 250 μg/L diazinon and observed significant AChE 

inhibition accompanied by decreased swimming speed, demonstrating association between 

diazinon-induced AChE inhibition and a specific behavioral effect in fish. 

 Based on these short-term laboratory exposure results, many authors have speculated that 

since fish feeding, defense, schooling, spawning and migration are significantly influenced by 

olfactory cues, disruption of this sensory function would place the organism at a competitive 

disadvantage in the natural environment. However, an important aspect of the findings to date is 

that the effects are, for the most part, reversible. Once the animal is removed from the chemical 

exposure, recovery was observed for the vast majority of the chemicals evaluated. In addition, 

some studies showed that over an extended exposure period, the fish adapted to the chemicalinduced change by partially regenerating lost cells or damaged neurons leading to partial 

recovery of normal olfactory function. 

 In the absence of confirmatory field exposure studies, whether effects of chemicals on the 

olfactory system structures or function of aquatic organisms result in adverse outcomes cannot 

be substantiated (no articles were obtained that evaluated this issue). The primary unanswered 

question is whether temporary damage to olfactory structures or loss of olfactory function affect 

homing, migratory patterns, feeding activity of exposed organisms in the wild, and more 

importantly, whether these behavioral changes affect the ability of the exposed population to 

reproduce, grow and ultimately survive in the wild. The impact of sublethal effects on the longterm survival of an exposed aquatic population is difficult to determine from laboratory studies. 

Long-term, field and laboratory studies are needed to provide the weight of evidence necessary 

to use such endpoints in risk assessment and criteria derivation. However, it should be noted that 

the freshwater and saltwater criteria recommended in this document are below the concentrations 

reported to affect a variety of olfactory endpoints in several salmonid species. 
23

7. UNUSED DATA 

 Data from some studies were not used in this document, as they did not meet the criteria for 

inclusion as specified in the Guidelines (Stephan et al. 1985). The reader is referred to the 

Guidelines for further information regarding these criteria. 

Studies were Conducted with Species that are Not Resident in North America 

Alabaster (1969) 

Alam and Maughan (1993) 

Alam et al. (1995) 

Anees (1974, 1976, 1978) 

Arab et al. (1990) 

Asaka et al. (1980) 

Bajpai and Perti (1969) 

Boumaiza et al. (1979) 

Ceron et al. (1996a,b) 

Chu and Lau (1994) 

El-Elaimy et al. (1990) 

Ferrando et al. (1991) 

Hamm et al. (1998) 

Hidaka et al. (1984) 

Hirayama and Tamanoi (1980) 

Hirose and Kawakami (1977) 

Hirose and Kitsukama (1976) 

Hirose et al. (1979) 

Iqbal et al. (1992) 

Kabir and Ahmed (1979) 

Kabir and Begum (1978) 

Kanazawa (1975, 1980, 1981a,b, 

1983a) 

Khalaf-Allah (1999) 

Kikuchi et al. (1992) 

Kimura and Keegan (1966) 

Kobayashi et al. (1993) 

Miah et al. (1995) 

Morale et al. (1998) 

Niforos and Lim (1998) 

Nishiuchi and Yoshida (1972) 

Rompas et al. (1989) 

Sakr and Gabr (1992) 

Sakr et al. (1991) 

Sancho et al. (1992a,b, 1993a,b, 

1994) 

Setakana and Tan (1991) 

Shigehisa and Shiraishi (1998) 

Sinha et al. (1987) 

Stevens (1991, 1992) 

Stevens and Warren (1992) 

Tsuda et al. (1989, 1992, 1995a,b, 

1997a,b) 

Uno et al. (1997) 

Van der Geest et al. (1999) 

Yasutomi and Takahashi (1987)

Data were Compiled from Other Sources 

Bay et al. (1993) 

Connolly (1985) 

Dyer et al. (1997) 

Eisler (1986) 

Garten and Trabalka (1983) 

Kaiser et al. (1997) 

Kanazawa (1982) 

Kenaga (1979, 1982) 

Robinson (1999) 

Roex et al. (2000) 

Steen et al. (1999) 

Van der Geest et al. (1997) 

Vighi and Calamari (1987) 

Vittozzi and DeAngelis (1991) 

Yoshioka et al. (1986) 

Zaroogian et al. (1985a)
24 

Diazinon was a Component of a Drilling Mud, Effluent, Mixture, Sediment or Sludge 

Alam and Maughan (1992) 

Amato et al. (1992) 

Bailey et al. (1996, 2000) 

Bathe et al. (1975a,b) 

Bishop et al. (1999) 

Burchfield and Storrs (1954) 

Burkhard and Jenson (1993) 

Deanovic et al. (1996, 1997) 

Dennis et al. (1979a,b) 

DeVlaming et al. (2000) 

Doggett and Rhodes (1991) 

Duursma and Hanafi (1975) 

Foe (1995) 

Foe et al. (1998) 

Glass et al. (1995) 

Gruber and Munn (1998) 

Hashimoto et al. (1982) 

Hatakeyama et al. (1997) 

Hendriks et al. (1998) 

Hilsenhoff (1959) 

Kikuchi et al. (1996) 

Kuivila and Foe (1995) 

LaBrecque et al. (1956) 

Larsen et al. (1998) 

Lehotay et al. (1998) 

McLeay and Hall (1999) 

Macek (1975) 

Malone and Blaylock (1970) 

Matsuo and Tamura (1970) 

Mazidji et al. (1990) 

Mulla et al. (1963) 

Nishiuchi (1977) 

Pan and Dutta (1998) 

Rettich (1979) 

Singh (1973) 

Steinberg et al. (1992) 

Tripathi (1992) 

Tsuda et al. (1997a,b) 

Verma et al. (1982) 

Werner et al. (2000) 

Wong (1997) 

Wong and Chang (1988)

 Results of tests conducted with brine shrimp, Artemia sp. (e.g. Kuwabara et al. 1980), 

were not used because these species are from a unique saltwater environment. 

 Results were not used when either the test procedures, test material, or dilution water was 

not adequately described (e.g., Adlung 1957; Ansari et al. 1987; Butler et al. 1975a,b; 

Chatterjee 1975; Hashimoto and Fukami 1969; Hatakeyama and Sugaya 1989; Kaur and Toor 

1980; Murray and Guthrie 1980; Oh et al. 1991; Qadri and Anjum 1982). 

 Results of some laboratory tests were not used because the tests were conducted in 

distilled or deionized water without addition of appropriate salts or were conducted in 

chlorinated or “tap” water (e.g., Mulla et al. 1962; Rettich 1977; Yasuno et al. 1965), or the 

concentration of a water-miscible solvent used to prepare the test solution exceeded 0.5 mL/L 

(Beauvais et al. 2000). Hirakoso 1968; Lee et al. 1993; Jamnback and Frempong-Boadu 1966; 

Klassen et al. 1965; Kok 1972; Lilly et al. 1969; Mulla 1963; Nishiuchi and Asano 1979; 

O'Kelley and Deason 1976; Steinberg et al. 1993 were not used because the results were not 

adequately described or could not be interpreted. 

 Tests conducted without controls, with unacceptable control survival, or with too few test 

organisms were not used (e.g., Applegate et al. 1957; Devillers et al. 1985; Federle and Collins 

1976; Allison and Hermanutz 1977). Data of Norland et al. (1974) were not used because they 
25 

were derived using organisms preconditioned to organophosphorus chemicals. 

Experimental Model was Plasma, Enzymes, Tissue, or Cell Cultures 

Anjum and Siddiqui (1990) 

Ansari and Kumar (1988) 

Ariyoshi et al. (1990) 

Burbank and Snell (1994) 

Christensen and Tucker (1976) 

Dutta et al. (1992a,b, 1993, 

 1994, 1997) 

Dyer et al. (1993) 

Fujii and Asaka (1982) 

Garrood et al. (1990) 

Hiltibran (1974) 

Keizer et al. (1995) 

Kraus (1985) 

Mitsuhashi et al. (1970) 

Moore and Waring (1996) 

Olson and Christensen (1980) 

Qadri and Dutta (1995) 

Sastry and Malik (1982a,b) 

Sastry and Sharma (1980, 

1981) 

Vigfusson et al. (1983) 

Weiss (1959, 1961) 

Weiss and Gakstater (1964) 

Whitmore and Hodges (1978)

 BCFs and BAFs from laboratory tests were not used when the tests were static or when 

the concentration of diazinon in the test solution was not adequately measured or varied too 

much (e.g., Khattat and Farley 1976). Toxicity data were not used if they were generated with 

a photoluminescence assay utilizing lyophilized marine bacteria that had been rehydrated (e.g., 

Curtis et al. 1982). Reports of the concentration of diazinon in wild aquatic organisms (e.g., 

Clark et al. 1984) were not used to calculate BAFs when either the number of measurements of 

the concentration in water was too small or the range of the measured concentrations in water 

was too large. BCFs obtained from microcosm or model ecosystem studies were not used 

when the concentration of diazinon in water decreased with time (e.g., Miller et al. 1966). 
26 

8. SUMMARY 

8.1. Freshwater Data 

 The acute toxicity of diazinon to freshwater organisms was determined for 13 invertebrate 

species from 11 genera, 10 fish species from 8 genera, and one amphibian species (Figure 1 

and Table 3). Nine of the invertebrate species (seven crustaceans and two insects) were the 

most sensitive organisms tested (SMAV = 0.38 to 25 μg/L) and one invertebrate species 

(planarian) was the most tolerant species tested (SMAV = 11,640 μg/L). Freshwater fish and 

the amphibian (green frog) were intermediate in sensitivity to the two groups of invertebrates. 

Rainbow trout (Oncorhynchus mykiss) was the most sensitive (SMAV = 425.8 μg/L) and 

goldfish (Carassius auratus) was the most tolerant fish tested (SMAV = 9,000 μg/L). No 

relationships have been demonstrated between diazinon toxicity and water quality 

characteristics such as hardness. The freshwater Final Acute Value is 0.3397 μg/L. 

 The chronic toxicity of diazinon to freshwater organisms was determined for four species 

(Figure 3 and Table 2). Chronic values ranged from 0.3382 to 68.93 μg/L (Table 2), and the 

Acute-Chronic Ratios (ACRs) ranged from 1.112 for Ceriodaphnia dubia to > 903.8 for brook 

trout (Salvelinus fontinalis) (Table 3). The Final Acute-Chronic Ratio for diazinon was 

derived using two ACRs for tested species with acute values near the FAV (C. dubia and A. 

bahia) because the ACRs decreased with SMAVs. The calculated FACR was less than 2.0, 

indicating that the organisms may have become acclimated to diazinon during the study. 

Therefore, the FACR value was changed to 2.0 (Stephan et al. 1985). Thus, the freshwater 

Final Chronic Value (FCV) for diazinon is 0.1699 μg/L (FAV ÷ FACR, or 0.3397 μg/L ÷ 2.0 = 

0.1699 μg/L). 

8.2. Saltwater Data 

 The acute toxicity of diazinon to saltwater organisms was determined for 7 invertebrate 

species from 7 genera and 2 fish species from 2 genera (Figure 2 and Table 3). Five of the 

invertebrates were crustaceans and the most sensitive species tested (SMAV = 2.57 to 21 μg/L) 

and two species (an annelid and an echinoderm) were the most tolerant species tested (SMAVs 

> 2,880 and > 9,600 μg/L, respectively). The two saltwater fish species tested were 

intermediate in sensitivity with acute values of 1,170 and 1,400 μg/L. No relationships have 

been demonstrated between diazinon toxicity and water quality characteristics such as salinity. 
27 

The saltwater Final Acute Value is 1.637 μg/L. 

 Chronic values were determined for two species of saltwater organisms (Figure 3 and 

Table 2). The mysid, Americamysis bahia, and the sheepshead minnow, Cyprinodon 

variegatus, had chronic values of 3.040 and < 0.47 μg/L, respectively (Table 2). ACRs for 

these speces were 1.586 for the mysid and > 2,979 for the sheepshead minnow (Table 3). The 

Final Acute-Chronic Ratio for diazinon was derived using two ACRs for tested species with 

acute values near the FAV (C. dubia and A. bahia) because the ACRs decreased with SMAVs. 

The calculated FACR was less than 2.0, indicating that the organisms may have become 

acclimated to diazinon during the study. Therefore, the FACR value was changed to 2.0 

(Stephan et al. 1985). Thus, the saltwater Final Chronic Value (FCV) for diazinon is 0.8185 

μg/L (FAV ÷ FACR, or 1.637 μg/L ÷ 2.0 = 0.8185 μg/L). 

8.3. Plant Data 

 Only one acceptable test with a freshwater algal species (Selenastrum capricornutum) was 

available, whereas no acceptable toxicity data are available for freshwater vascular plants. No 

saltwater tests with aquatic plants were suitable for consideration when estimating the Final 

Plant Value. Therefore, based on the single test with the freshwater algae, the Final Plant 

Value is 6,400 μg/L. 

8.4. Bioaccumulation Data 

 Bioaccumulation of diazinon was measured in three species of freshwater fish and steadystate concentrations were reached in about three days. Bioconcentration factors of 62, 120 and 

188 were determined for rainbow trout, carp (Cyprinus carpio) and guppy (Poecilia 

reticulata), respectively. The tissue half-life of diazinon was less than seven days. 

Bioaccumulation of diazinon was determined in one saltwater species. The sheepshead 

minnow was exposed for 108 days to three concentrations of diazinon. The mean 

bioconcentration factor, based on the BCF for the three concentrations, was 169. 
28 

9. NATIONAL CRITERIA 

9.1. Freshwater

 The procedures described in the “Guidelines for Deriving Numerical National Water 

Quality Criteria for the Protection of Aquatic Organisms and Their Uses” (Stephan et al. 1985) 

indicate that, except possibly where a locally important species is very sensitive, freshwater 

aquatic organisms and their uses should not be affected unacceptably if the one-hour average 

concentration does not exceed 0.17 μg/L more than once every three years on the average and 

if the four-day average concentration of diazinon does not exceed 0.17 μg/L more than once 

every three years on the average. 

 Growth of offspring of exposed brook trout, a recreationally important freshwater fish 

species, was statistically significantly reduced by 40% at the lowest tested concentration of 0.8 

μg/L, which is a factor of 4.7 times the CCC. However, the chronic value for this study is a 

less than value and it is uncertain how close to the freshwater CCC adverse effects may occur. 

9.2. Saltwater 

 The procedures described in the “Guidelines for Deriving Numerical National Water 

Quality Criteria for the Protection of Aquatic Organisms and Their Uses” (Stephan et al. 1985) 

indicate that, except possibly where a locally important species is very sensitive, saltwater 

aquatic organisms and their uses should not be affected unacceptably if the one-hour average 

concentration does not exceed 0.82 μg/L more than once every three years on the average and 

if the four-day average concentration of diazinon does not exceed 0.82 μg/L more than once 

every three years on the average. 

 Reproduction of the saltwater sheepshead minnow was statistically significantly 

reduced by 31% at the lowest tested concentration of 0.47 μg/L, which is below the saltwater 

CCC. Therefore, where exposure to diazinon at or near CCC levels may occur to this or 

similar saltwater fish species, states and tribes may want to consider site-specific criteria 

derivations for diazinon. Because sensitive saltwater animals appear to have a narrow range of 

acute susceptibilities to diazinon, this criterion will probably be as protective as intended only 

when the magnitude and/or duration of excursions are appropriately small. 
29 

10. IMPLEMENTATION 

 As discussed in the Water Quality Standards Regulation (U.S. EPA 1983) and the 

Foreword to this document, a water quality criterion for aquatic life has regulatory impact only 

after it has been adopted in a state or tribal water quality standard. Such a standard specifies a 

criterion for a pollutant that is consistent with a particular designated use. With the 

concurrence of the U.S. EPA, states and tribes designate one or more uses for each body of 

water or segment thereof and adopt criteria that are consistent with the use(s) (U.S. EPA 1994, 

1987). In each standard a state or tribe may adopt the national criterion, if one exists, or, if 

adequately justified, a site-specific criterion (if the site is an entire state, the site-specific 

criterion is also a state-specific criterion). 

 Site-specific criteria may include not only site-specific criterion concentrations (U.S. EPA 

1994), but also site-specific, and possibly pollutant-specific, durations of averaging periods and 

frequencies of allowed excursions (U.S. EPA 1991). The averaging periods of “one hour” and 

“four days” were selected by the U.S. EPA on the basis of data concerning how rapidly some 

aquatic species react to increases in the concentrations of some pollutants, and “three years” is 

the Agency’s best scientific judgment of the average amount of time aquatic ecosystems 

should be provided between excursions (Stephan et al. 1985; U.S. EPA 1991). However, 

various species and ecosystems react and recover at greatly different rates. Therefore, if 

adequate justification is provided, site-specific and/or pollutant-specific concentrations, 

durations, and frequencies may be higher or lower than those given in national water quality 

criteria for aquatic life. 

 Use of criteria, which have been adopted into state or tribal water quality standards, for 

developing water quality-based permit limits requires selection of an appropriate wasteload 

allocation model. Although dynamic models are preferred for the application of these criteria 

(U.S. EPA 1991), limited data or other considerations might require the use of a steady-state 

model (U.S. EPA 1986). Guidance on mixing zones and the design of monitoring programs is 

also available (U.S. EPA 1987, 1991). 
30 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Genus Mean Acute Values

0.01

0.1

1

10

100

1000

104

105

Diazinon Effect Concentration (μg/L)

Figure 1. Summary of Ranked Diazinon GMAVs

Freshwater

 Fish

 Invertebrates

 Amphibians

Freshwater Final Acute Value = 0.3397 μg/L Diazinon

Criteria Maximum Concentration = 0.1699 μg/L Diazinon

(Cumulative Fraction)
31 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Genus Mean Acute Values

0.1

1

10

100

1000

104

Diazinon Effect Concentration (μg/L)

Figure 2. Summary of Ranked Diazinon GMAVs

Saltwater

 Fish

 Invertebrates

Saltwater Final Acute Value = 1.637 μg/L Diazinon

Criteria Maximum Concentration = 0.8185 μg/L Diazinon

(Cumulative Fraction)
32 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Genus Mean Chronic Values

0.01

0.1

1

10

100

1000

Diazinon Effect Concentration (μg/L)

Figure 3. Chronic Toxicity of Diazinon to Aquatic Animals

 Freshwater Inv ertebrates

 Freshwater Fish

 Saltwater Inv ertebrates

 Saltwater Fish

Saltwater Final Chronic Value = 0.8185 μg/L Diazinon

Freshwater Final Chronic Value = 0.1699 μg/L Diazinon

(Cumulative Fraction)
33 

Table 1. Acute Toxicity of Diazinon to Aquatic Animals 

Species Methoda Chemicalb

Hardness 

(mg/L as 

CaCO3) 

LC50 

or EC50 

(μg/L)

Species Mean 

Acute Valuec 

(μg/L) Reference

FRESHWATER SPECIES

Planaria, 

Dugesia tigrina 

S, M Technical 

(85%) 

46.5-47.5 11,640 11,640 Phipps 1988 

Oligochaete worm, 

Lumbriculus 

variegates 

S, M Technical 

(85%) 

46-48 9,980 - Phipps 1988 

Oligochaete worm, 

Lumbriculus 

variegates 

S, U Technical 

(95%) 

42-47 6,160 7,841 Ankley and 

Collyard 1995 

Snail (2.4 g), 

Gillia altilis 

S, U Technical 

(89%) 

22-35 11,000 11,000 Robertson and 

Mazzella 1989 

Apple snail (1-day), 

Pomacea paludosa 

F, M Technical 

(87%) 

130.5 2,950 - Call 1993 

Apple snail (7-days), 

Pomacea paludosa 

F, M Technical 

(87%) 

219 3,270 - Call 1993 

Apple snail (7-days), 

Pomacea paludosa 

F, M Technical 

(87%) 

173.5 3,390 3,198 Call 1993 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

40 0.57d,e - Norberg-King 

1987 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

45 0.66d,e - Norberg-King 

1987 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

40-48 0.57 d,e - Norberg-King 

1987 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- >1.0 d,e - Norberg-King 

1987 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

40 >0.6 d,e - Norberg-King 

1987 

Cladoceran 

(<6 hr), 

Ceriodaphnia dubia 

S, M Technical 

(85%) 

40 0.66 d,e - Norberg-King 

1987 

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.35 - Norberg-King 

1987 
Table 1. (continued) 

34 

Species Methoda Chemicalb

Hardness 

(mg/L as 

CaCO3) 

LC50 

or EC50 

(μg/L)

Species Mean 

Acute Valuec 

(μg/L) Reference

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.35 - Norberg-King 

1987 

Cladoceran 

(<6 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.25 - Norberg-King 

1987 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.33 - Norberg-King 

1987 

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.35 - Norberg-King 

1987 

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.59 - Norberg-King 

1987 

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.43 - Norberg-King 

1987 

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.35 - Norberg-King 

1987 

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(85%) 

- 0.36 - Norberg-King 

1987 

Cladoceran 

(<48 hr), 

Ceriodaphnia dubia 

S, U Technical 

(95%) 

40-48 0.5 - Ankley et al. 

1991 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, M Analytical 

(99%) 

80-100 0.58 - Bailey et al. 1997 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, M Analytical 

(99%) 

80-100 0.48 - Bailey et al. 1997 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, M Analytical 

(99%) 

80-100 0.26 - Bailey et al. 1997 

Cladoceran 

(<24 hr), 

Ceriodaphnia dubia 

S, M Analytical 

(99%) 

80-100 0.29 0.3773 Bailey et al. 1997 

Cladoceran 

(<20 hr), 

Daphnia magna 

S, U Technical 50 0.96 - Vilkas 1976 
Table 1. (continued) 

35 

Species Methoda Chemicalb

Hardness 

(mg/L as 

CaCO3) 

LC50 

or EC50 

(μg/L)

Species Mean 

Acute Valuec 

(μg/L) Reference

Cladoceran 

(<24 hr), 

Daphnia magna 

S, U Analytical 200 1.5 - Dortland 1980 

Cladoceran 

(<48 hr), 

Daphnia magna 

S, U Technical 

(95%) 

40-48 0.8 1.048 Ankley et al. 

1991 

Cladoceran 

(first instar), 

Daphnia pulex 

S, U Technical 

(89%) 

47 0.90 - Cope 1965a; 

Sanders and Cope 

1966 

Cladoceran 

(first instar), 

Daphnia pulex 

S, U Technical 

(89%) 

47 0.8 - Johnson and 

Finley 1980; 

Mayer and 

Ellersieck 1986 

Cladoceran 

(<48 hr), 

Daphnia pulex 

S, U Technical 

(95%) 

40-48 0.65 0.7764 Ankley et al. 

1991 

Cladoceran 

(first instar), 

Simocephalus 

serrulatus 

S, U Technical 

(89%) 

47 1.8 - Cope 1965a; 

Sanders and Cope 

1966; Mayer and 

Ellersieck 1986 

Cladoceran 

(first instar), 

Simocephalus 

serrulatus 

S, U Technical 

(89%) 

47 1.4 1.587 Sanders and Cope 

1966; Johnson 

and Finley 1980; 

Mayer and 

Ellersieck 1986 

Amphipod (mature), 

Gammarus fasciatus 

S, U Technical 

(89%) 

44 2.04 2.04 Johnson and 

Finley 1980; 

Mayer and 

Ellersieck 1986 

Amphipod (mature), 

Gammarus 

pseudolimnaeus 

R, M Analytical 

(100%) 

62.5 16.82 16.82 Hall and 

Anderson 2004 

Amphipod 

(7-14 days), 

Hyalella azteca 

S, U Technical 

(95%) 

42-47 6.51 6.51 Ankley and 

Collyard 1995 

Stonefly 

(larva 30-35 mm), 

Pteronarcys 

californica

S, U Technical 

(89%) 

47 25 25 Cope 1965a; 

Sanders and Cope 

1968; Johnson 

and Finley 1980; 

Mayer and 

Ellersieck 1986 
Table 1. (continued) 

36 

Species Methoda Chemicalb

Hardness 

(mg/L as 

CaCO3) 

LC50 

or EC50 

(μg/L)

Species Mean 

Acute Valuec 

(μg/L) Reference

Midge 

(third instar), 

Chironomus tentans 

S, U Technical 

(95%) 

42-47 10.7 10.7 Ankley and 

Collyard 1995 

Cutthroat trout 

(2.0 g), 

Oncorhynchus clarki

S, U Technical 

(92%) 

162 1,700 - Johnson and 

Finley 1980; 

Mayer and 

Ellersieck 1986 

Cutthroat trout 

(2.0 g), 

Oncorhynchus clarki

S, U Technical 

(92%) 

44 2,760 2,166 Mayer and 

Ellersieck 1986 

Rainbow trout 

(3.7 cm), 

Oncorhynchus 

mykiss 

S, U Technical - 400 - Beliles 1965 

Rainbow trout 

(1.20 g), 

Oncorhynchus 

mykiss 

S, U Technical 

(89%) 

44 90 - Cope 1965a; 

Johnson and 

Finley 1980; 

Mayer and 

Ellersieck 1986 

Rainbow trout 

(25-50 g), 

Oncorhynchus 

mykiss 

S, U Technical - 3,200 - Bathe et al. 1975a 

Rainbow trout, 

Oncorhynchus 

mykiss 

S, U Technical - 90 - Ciba-Giegy 1976 

Rainbow trout, 

Oncorhynchus 

mykiss 

S, U Reagent 192 1,350 425.8 Meier et al. 1979; 

Dennis et al. 1980 

Brook trout (1 yr), 

Salvelinus fontinalis 

F, M Technical 

(92.5%) 

45 800 - Allison and 

Hermanutz 1977 

Brook trout (1 yr), 

Salvelinus fontinalis 

F, M Technical 

(92.5%) 

45 450 - Allison and 

Hermanutz 1977 

Brook trout (1 yr), 

Salvelinus fontinalis 

F, M Technical 

(92.5%) 

45 1,050 723.0 Allison and 

Hermanutz 1977 

Lake trout (3.20 g), 

Salvelinus 

namaycush 

S, U Technical 

(92%) 

162 602 602 Johnson and 

Finley 1980; 

Mayer and 

Ellerseick 1986 

Zebrafish (0.4 g), 

Danio rerio 

R, M Technical 

(98%) 

- 8,000 8,000 Keizer et al. 1991 
Table 1. (continued) 

37 

Species Methoda Chemicalb

Hardness 

(mg/L as 

CaCO3) 

LC50 

or EC50 

(μg/L)

Species Mean 

Acute Valuec 

(μg/L) Reference

Fathead minnow, 

Pimephales promelas 

S, U Reagent 192 10,300e

 - Meier et al. 1979; 

Dennis et al. 1980 

Fathead minnow 

(newly hatched 

larva), 

Pimephales promelas 

S, M Technical 

(87.1%) 

(fresh stock 

solution) 

45.8 4,300 e - Jarvinen and 

Tanner 1982 

Fathead minnow 

(newly hatched 

larva), 

Pimephales promelas 

S, M Technical 

(87.1%) 

(aged stock 

solution) 

45.8 2,100 e - Jarvinen and 

Tanner 1982 

Fathead minnow 

(juvenile), 

Pimephales promelas 

F, M Technical 

(92.5%) 

45 6,600 Allison and 

Hermanutz 1977 

Fathead minnow 

(juvenile), 

Pimephales promelas 

F, M Technical 

(92.5%) 

45 6,800 Allison and 

Hermanutz 1977 

Fathead minnow 

(juvenile), 

Pimephales promelas 

F, M Technical 

(92.5%) 

45 10,000 - Allison and 

Hermanutz 1977 

Fathead minnow 

(newly hatched 

larva), 

Pimephales promelas 

F, M Technical 

(87.1%) 

45 6,900 - Jarvinen and 

Tanner 1982 

Fathead minnow 

(juvenile), 

Pimephales promelas 

F, M Technical 

(87.1%) 

43.6 9,350 7804 University of 

WisconsinSuperior 1988 

Goldfish 

(2.5-6.0 cm), 

Carassius auratus 

S, U Technical 

(91%) 

- 9,000 9,000 Beliles 1965 

Flagfish (6 wk), 

Jordanella floridae 

F, M Technical 

(92.5%) 

45 1,500 - Allison and 

Hermanutz 1977 

Flagfish (7 wk), 

Jordanella floridae 

F, M Technical 

(92.5%) 

45 1,800 1,643 Allison and 

Hermanutz 1977 

Guppy (0.6 g), 

Poecilia reticulata 

R, M Technical 

(98%) 

- 800 800 Keizer et al. 1991 

Bluegill 

(2.5-5.0 cm), 

Lepomis macrochirus 

S, U Technical - 136e

 - Beliles 1965 

Bluegill (0.87 g), 

Lepomis macrochirus 

S, U Technical - 22 e - Cope 1965b 
Table 1. (continued) 

38 

Species Methoda Chemicalb

Hardness 

(mg/L as 

CaCO3) 

LC50 

or EC50 

(μg/L)

Species Mean 

Acute Valuec 

(μg/L) Reference

Bluegill, 

Lepomis macrochirus 

S, U Technical - 22 e - Ciba-Geigy 1976 

Bluegill (0.8 g), 

Lepomis macrochirus 

S, U Reagent 192 120 e - Meier et al. 1979; 

Dennis et al. 1980 

Bluegill (1.00 g), 

Lepomis macrochirus 

S, U Technical 

(92%) 

44 168.0 e - Johnson and 

Finley 1980; 

Mayer and 

Ellersieck 1986 

Bluegill (1 yr.), 

Lepomis macrochirus 

F, M Technical 

(92.5%) 

45 480 - Allison and 

Hermanutz 1977 

Bluegill (1 yr.), 

Lepomis macrochirus 

F, M Technical 

(92.5%) 

45 440 459.6 Allison and 

Hermanutz 1977 

Green frog 

(stage 8), 

Rana clamitans 

R, U Technical - >50 >50 Harris et al. 1998 

Species Methoda Chemicalb

Salinity 

 (g/kg) 

LC50 

or EC50 

 (μg/L) 

Species Mean 

Acute Valuec 

(μg/L) Reference

SALTWATER SPECIES

Annelid worm 

(juvenile), 

Neanthes 

arenaceodentata

R, U (96%) 30 >2,880 >2,880 Thursby & Berry 

1988 

Copepod (adult), 

Acartia tonsa

S, M Technical 

(97.6%) 

20 2.57 2.57 Khattat & Farley 

1976 

Mysid (juvenile), 

Americamysis bahia

R, U (96%) 29 8.5 e - Thursby & Berry 

1988 

Mysid (juvenile), 

Americamysis bahia

S, U Technical 25 8.5 e - Cripe 1994 

Mysid (juvenile), 

Americamysis bahia

F, M Diazinon 17 4.82 4.82 Nimmo et al. 1981 

Amphipod (juvenile), 

Ampelisca abdita

R, U (96%) 30 6.6 6.6 Thursby & Berry 

1988 

Pink shrimp (larval), 

Penaeus duorarum

S, U Technical 25 21 21 Cripe 1994 

Grass shrimp 

(larval), 

Palaemonetes pugio

R, U (96%) 30 2.8 2.8 Thursby & Berry 

1988 
Table 1. (continued) 

39 

Species Methoda Chemicalb

Salinity 

 (g/kg) 

LC50 

or EC50 

 (μg/L) 

Species Mean 

Acute Valuec 

(μg/L) Reference

Sea urchin 

(embryo/larval), 

Arbacia punctulata

S, U (96%) 31 >9,600 >9,600 Thursby & Berry 

1988 

Sheepshead minnow 

(juvenile), 

Cyprinodon 

variegatus

F, M (92.6%) 23 1,400 1,400 Goodman et al. 

1979; Mayer 1987 

Inland silverside 

(juvenile), 

Menidia beryllina

R, U (96%) 30 1,170 1,170 Thursby & Berry 

1988 

a

 S = static; R = renewal; F = flow-through; M = measured; U = unmeasured. 

b

 Percent purity is given in parenthesis when available. 

c

 Species Mean Acute Value was calculated from the underlined number(s) in the preceeding column. 

d

 Animals were fed during the exposure. e

 Results were not used in the calculation of the Species Mean Acute Value due to availability of data from more 

sensitive test conditions.
40 

Table 2. Chronic Toxicity of Diazinon to Aquatic Animals

Species Testa Chemicalb

Hardness 

(mg/L as 

 CaCO3) 

Chronic 

Limits 

 (μg/L)__

Chronic 

Value 

 (μg/L)__ Reference

FRESHWATER SPECIES

Cladoceran 

(<6-hr. old), 

Ceriodaphnia 

dubia

LC 

(7-day) 

Technical 

(85%) 

40 0.220-0.520 0.3382 Norberg-King 1987 

Brook trout 

(yearling), 

Salvelinus 

fontinalis

PLC Technical 

(92.5%) 

45 0-0.8 < 0.8 Allison and 

Hermanutz 1977 

Fathead minnow 

(embryo-larva), 

Pimephales 

promelas

ELS Technical 

(88.2%) 

44-49 16.5-37.8 24.97 Norberg-King 1989 

Fathead minnow 

(embryo-larva), 

Pimephales 

promelas

ELS Technical 

(87.1%) 

45.8 50-90 67.08 Jarvinen and Tanner 

1982 

Flagfish 

(1-day old), 

Jordanella floridae

LC - - 54-88 68.93 Allison 1977 

SALTWATER SPECIES

Mysid (juvenile), 

Americamysis 

bahia

LC - 30-31c

 2.1-4.4 3.040 Nimmo et al. 1981 

Sheepshead 

minnow (juvenile), 

Cyprinodon 

variegatus

PLC Technical 

(92.6%) 

16.5c

 0-0.47 < 0.47 Goodman et al. 

1979 

a

 PLC = partial life-cycle; ELS = early life-stage; LC = life cycle. 

b

 Percent purity is listed in parentheses when available. 

c

 Salinity (g/kg). 
Table 2. (continued) 

41 

Acute-Chronic Ratio

Species

Hardness 

(mg/L as 

CaCO3)

Acute 

Value 

 (μg/L)_

Chronic Value 

 (μg/L)__ Ratio

Mean 

Ratio

 

Cladoceran, 

Ceriodaphnia dubia

40 0.3760 0.3382 1.112 1.112 

Mysid, 

Americamysis bahia

17c

 4.82 3.040 1.586 1.586 

Flagfish, 

Jordanella floridae

45 1,643 68.93 23.84 23.84 

Fathead minnow, 

Pimephales promelas

44-49 9,350 24.97 374.4 - 

Fathead minnow, 

Pimephales promelas

45.8 6,900 67.08 102.9 196.3 

Brook trout, 

Salvelinus fontinalis

45 723.0 <0.8 >903.8 >903.8 

Sheepshead minnow, 

Cyprinodon variegatus

16.5c

 1,400 <0.47 >2,979 >2,979 

 

c

 Salinity (g/kg).
42 

Table 3. Ranked Genus Mean Acute Values with Species Mean Acute-Chronic Ratios

Ranka

Genus Mean 

Acute Value 

 (μg/L)__ Species

Species Mean 

Acute Value 

 (μg/L)b_

Species Mean 

Acute-Chronic 

 Ratioc,d_

FRESHWATER SPECIES

20 11,640 Planaria, 

Dugesia tigrina

11,640 - 

19 11,000 Snail, 

Gillia altilis

11,000 - 

18 9,000 Goldfish, 

Carassius auratus

9,000 - 

17 8,000 Zebrafish, 

Danio rerio

8,000 - 

16 7,841 Oligachaete worm, 

Lumbricus variegatus

7,841 - 

15 7804 Fathead minnow, 

Pimephales promelas

7804 196.3 

14 3,198 Snail, 

Pomacea paludosa

3,198 - 

13 1,643 Flagfish, 

Jordanella floridae

1,643 23.84 

12 960.4 Cutthroat trout, 

Oncorhynchus clarki

2,166 - 

 Rainbow trout, 

Oncorhynchus mykiss

425.8 - 

11 800 Guppy, 

Poecilia reticulata

800 - 

10 659.7 Brook trout, 

Salvelinus fontinalis

723 > 903.8 

 Lake trout, 

Salvelinus namaycush

602 - 

9 459.6 Bluegill, 

Lepomis macrochirus

459.6 - 
Table 3. (continued) 

43 

Ranka

Genus Mean 

Acute Value 

 (μg/L)__ Species

Species Mean 

Acute Value 

 (μg/L)b_

Species Mean 

Acute-Chronic 

 Ratioc,d_

8 >50 Green frog 

Rana clamitans

>50 - 

7 25 Stonefly, 

Pteronarcys 

californica

25 - 

6 10.7 Midge, 

Chironomus tentans

10.7 - 

5 6.51 Amphipod, 

Hyalella azteca

6.51 - 

4 5.858 Amphipod, 

Gammarus fasciatus

2.04 - 

 Amphipod, 

Gammarus 

pseudolimnaeus

16.82 - 

3 1.587 Cladoceran, 

Simocephalus 

serrulatus

1.587 - 

2 0.9020 Cladoceran, 

Daphnia magna

1.048 - 

 Cladoceran, 

Daphnia pulex

0.7764 - 

1 0.3773 Cladoceran, 

Ceriodaphnia dubia

0.3773 1.112
Table 3. (continued) 

44 

SALTWATER SPECIES

9 >9,600 Sea urchin, 

Arbacia punctulata 

>9,600 - 

8 >2,880 Annelid worm, 

Neanthes 

arenaceodentata

>2,880 - 

7 1,400 Sheepshead minnow, 

Cyprinodon variegatus

1,400 >2,979 

6 1,170 Inland silverside, 

Menidia beryllina

1,170 - 

5 21 Pink shrimp, 

Penaeus duorarum

21 - 

4 6.6 Amphipod, 

Ampelisca abdita

6.6 - 

3 4.82 Mysid, 

Americamysis bahia

4.82 1.586

2 2.8 Grass shrimp 

Palaemonetes pugio

2.8 - 

1 2.57 Copepod, 

Acartia tonsa

2.57 - 

a

 Ranked from most sensitive to most resistant based on Genus Mean Acute Values. 

b

 From Table 1. 

c

 From Table 2. 

d

 The Species Mean Acute-Chronic Values underlined and in bold font were used to calculate 

the Final Acute-Chronic Ratio. 
Table 3. (continued) 

45 

Freshwater 

 Final Acute Value = 0.3397 μg/L 

 Criterion Maximum Concentration = 0.3397 μg/L ÷ 2 = 0.1699 μg/L 

 Final Acute-Chronic Ratio = 2.0 (see text) 

 Final Chronic Value = 0.3397 μg/L ÷ 2.0 = 0.1699 μg/L 

Saltwater 

 Final Acute Value = 1.637 μg/L 

 Criterion Maximum Concentration = 1.637 μg/L ÷ 2 = 0.8185 μg/L 

 Final Acute-Chronic Ratio = 2.0 (see text) 

 Final Chronic Value = 1.637 μg/L ÷ 2.0 = 0.8185 μg/L
46 

Table 4. Toxicity of Diazinon to Aquatic Plants 

Species

Hardness 

(mg/L as 

CaCO3)

Duration 

(days) Effect

Concentration 

 (μg/L)__ Reference

FRESHWATER SPECIES

Green algae, 

Selenastrum 

capricornutum

- 7 EC50 

(cell 

numbers) 

6,400 Hughes 

1988 
47 

Table 5. Bioaccumulation of Diazinon by Aquatic Organisms 

Species

Conc. in 

Water 

(μg/L)a

Duration

(days) Tissue

Percent 

Lipid

BCF or 

BAFb

Normalized 

BCF or BAFc Reference

FRESHWATER SPECIES

Rainbow trout 

(16 g), 

Oncorhynchus 

mykiss

15 14 Whole 

body 

- 62 - Seguchi and 

Asaka 1981 

Carp (8 g), 

Cyprinus 

carpio

15 14 Whole 

body 

- 120 - Seguchi and 

Asaka 

1981 

Guppy, 

Poecilia 

reticulata

350 14 Whole 

body 

- 188 - Keizer et al. 

1993 

SALTWATER SPECIES

Sheepshead 

minnow, 

Cyprinodon 

variegatus

1.8 108 Whole 

body 

(less brain) 

- 147 - Goodman et 

al. 1979 

Sheepshead 

minnow, 

Cyprinodon 

variegatus

3.5 108 Whole 

body 

(less brain) 

- 147 - Goodman et 

al. 1979 

Sheepshead 

minnow, 

Cyprinodon 

variegatus

6.5 108 Whole 

body 

(less brain) 

- 213 - Goodman et 

al. 1979 

a

 Measured concentration of diazinon. 

b

 Bioconcentration factors (BCFs) and bioaccumulation factors (BAFs) are based on measured 

 concentrations of diazinon in water and in tissue. 

c

 When possible, the factors were normalized to 1% lipids by dividing the BCFs and BAFs by 

 the percent lipids. 
48 

Table 6. Other Data on Effects of Diazinon on Aquatic Organisms

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

FRESHWATER SPECIES

Sewage 

microbes 

Regent - 22 hr No reduction of 

oxygen 

consumption 

40,000 Bauer et al. 1981 

Actinomycete 

bacteria 

Technical - 20 days Stimulated 

growth 

40,000 Sethunathan and 

MacRae 1969 

Green alga, 

Chlorella 

ellipsoidea

- - 72 hr Decreased ATP 

content 

100,000 Clegg and 

Koevenig 1974 

Green alga, 

Chlamydomonas

sp. 

- - 72 hr Decreased ATP 

content 

100,000 Clegg and 

Koevenig 1974 

Green alga, 

Scenedesmus 

quadricauda

- - 10 days No decrease in 

cell number, 

biomass, or 

photosynthesis 

1,000 Stadnyk and 

Campbell 1971 

Mixture of green 

alga and diatoms 

(99.9%) - 14 days Decreased growth <10 Butler et al. 

1975a 

Euglenoid, 

Euglena elastica

- - 72 hr Decreased ATP 

content 

100,000 Clegg and 

Koevenig 1974 

Duckweed, 

Wolffia 

papulifera

(97%) - 11 days Lethal 100,000 Worthley and 

Schott 1971 

Duckweed, 

Wolffia 

papulifera

(97%) - 11 days Teratogenic 

effects 

10,000 Worthley and 

Schott 1971 

Protozan, 

Paramecium 

caudatum

- - 1 hr LC50 3,000 Evtugyn et al. 

1997 

Rotifer, 

Brachionus 

calyciflorus

Technical 

(92%) 

80-100 24 hr LC50 29,220 FernandezCasalderrey et 

al. 1992a 

Rotifer 

(16-18 hr), 

Brachionus 

calyciflorus

Technical 

(92%) 

80-100 5 hr Reduced (50%) 

filtration and 

ingestion ratios 

14,000 FernandezCasalderrey et 

al. 1992b 

Rotifer (<2 hr), 

Brachionus 

calyciflorus

Technical 

(92%) 

80-100 10 days Decreased 

reproduction 

<5,000 FernandezCasalderrey et 

al. 1992c 
Table 6. (continued) 

49 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Rotifer (<2 hr), 

Brachionus 

calyciflorus

Technical 

(99%) 

80-100 4.04 days LT50 5,000 FernandezCasalderry et al. 

1992d 

Rotifer (<2 hr), 

Brachionus 

calyciflorus

Technical 

(99%) 

80-100 4.66 days LT50 7,000 FernandezCasalderrey et 

al. 1992d 

Rotifer (<2 hr), 

Brachionus 

calyciflorus

Technical 

(99%) 

80-100 2.49 days LT50 14,000 FernandezCasalderry et al. 

1992d 

Rotifer (<2 hr), 

Brachionus 

calyciflorus

- 80-100 48 hr NOEC 

Reproduction 

8,000 Snell and Moffat 

1992 

Rotifer (<2 hr), 

Brachionus 

calyciflorus

- 80-100 48 hr NOEC Ingestion 20,000 Juchelka and 

Snell 1994 

Oligochaete 

worm, 

Lumbriculus 

variegatus

- - 4 hr Lethal 20,000 Rogge and 

Drewes 1993 

Tubificid worm, 

Branchiura 

sowerbyi

- - 96 hr LC50 2,220 Chatterjee and 

Konar 1984 

Snail, 

(Physa acuta)

- - 48 hr LC50 4,800 Hashimoto and 

Nishiuchi 1981 

Cladoceran 

Daphnia magna

- 202 50 hr EC50 4.3 Anderson 1959 

Cladoceran 

(adult), 

Daphnia magna

- - 24 hr Adhesion of algal 

particles on 2nd 

antennae and 

immobilization 

1 Stratton and 

Corke 1981 

Cladoceran (<24 

hr), 

Daphnia magna

Analytical 

(95%) 

200 21 days Reduced 

reproduction and 

mobility 

0.3 Dortland 1980 

Cladoceran (<24 

hr), 

Daphnia magna

Analytical 

(99%) 

200 21 days No reduction in 

reproduction or 

mobility 

0.2 Dortland 1980 

Cladoceran (<24 

hr), 

Daphnia magna

Analytical 

(99%) 

200 21 days EC50 

(immobilization) 

0.22 Dortland 1980 

Cladoceran (<24 

hr), 

Daphnia magna

Analytical 

(99%) 

200 21 days EC50 

(immobilization) 

0.24 Dortland 1980 
Table 6. (continued) 

50 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Cladoceran (<24 

hr), 

Daphnia magna

Analytical 

(99%) 

200 21 days EC50 

(immobilization) 

0.7 Dortland 1980 

Cladoceran (<24 

hr), 

Daphnia magna

Analytical 

(99%) 

200 21 days EC50 

(immobilization) 

0.8 Dortland 1980 

Cladoceran (<24 

hr), 

Daphnia magna

Insecticidal 

soap 

- 48 hr LC50 0.74 Mitchell 1985 

Cladoceran (<24 

hr), 

Daphnia magna

Insecticidal 

soap 

- 96 hr LC50 0.21 Mitchell 1985 

Cladoceran 

(adult), 

Daphnia magna

Technical - 3 hr LC50 7.8 Nishiuchi and 

Hashimoto 1967 

Cladoceran, 

Daphnia magna

Technical - 3 hr LC50 80 Hashimoto and 

Nishiuchi 1981 

Cladoceran, 

Daphnia magna

Technical 

(92%) 

- 5 hr Reduced (50%) 

filtration rate 

0.47 FernandezCasalderrey et 

al. 1994 

Cladoceran (<24 

hr), 

Daphnia magna

Technical 

(92%) 

250 21 days NOEC survival 0.15 FernandezCasalderrey et 

al. 1995 

Cladoceran (<24 

hr), 

Daphnia magna

Technical 

(92%) 

250 21 days LOEC survival 0.18 FernandezCasalderrey et 

al. 1995 

Cladoceran (<24 

hr), 

Daphnia magna

Technical 

(92%) 

250 21 days LOEC 

reproduction 

0.15 FernandezCasalderrey et 

al. 1995 

Cladoceran (<24 

hr), 

Daphnia magna

Technical 

(92%) 

250 24 hr LC50 0.86 FernandezCasalderrey et 

al. 1995 

Cladoceran (<24 

hr), 

Daphnia magna

Technical 

(96.1%) 

182 21 days Reduced survival, 

growth and 

reproduction 

0.05 Sanchez et al. 

1998, 1999, 

2000 

Cladoceran, 

Daphnia magna

Optimum 160-180 30 min IC50 0.45 Fort et al. 1996 

Cladoceran, 

Daphnia pulex

- - 3 hr LC50 80 Hashimoto and 

Nishiuchi 1981 

Cladoceran, 

Daphnia pulex

- - 3 hr LC50 7.8 Nishiuchi and 

Hashimoto 1967 
Table 6. (continued) 

51 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Cladoceran 

(adult), 

Moina 

macrocopa

Technical - 3 hr LC50 26 Nishiuchi and 

Hashimoto 1967 

Cladoceran, 

Moina 

macrocopa

Technical - 3 hr LC50 50 Hashimoto and 

Nishiuchi 1981 

Copepod, 

Cyclops vividis

- - 96 hr LC50 2,600 Chatterjee and 

Konar 1984 

Amphipod 

(adult), 

Hyalella azteca

Technical 160-180 48 hr LC50 19 (measured) Werner and 

Nagel 1997 

Amphipod 

(0-2 days), 

Hyalella azteca

Technical 40 96 hr LC50 6.2 Collyard et al. 

1994 

Amphipod 

(2-4 days), 

Hyalella azteca

Technical 40 96 hr LC50 4.2 Collyard et al. 

1994 

Amphipod 

(6-8 days), 

Hyalella azteca

Technical 40 96 hr LC50 4.3 Collyard et al. 

1994 

Amphipod 

(8-10 days), 

Hyalella azteca

Technical 40 96 hr LC50 4.4 Collyard et al. 

1994 

Amphipod 

(12-14 days), 

Hyalella azteca

Technical 40 96 hr LC50 3.8 Collyard et al. 

1994 

Amphipod 

(16-18 days), 

Hyalella azteca

Technical 40 96 hr LC50 4.4 Collyard et al. 

1994 

Amphipod 

(20-22 days), 

Hyalella azteca

Technical 40 96 hr LC50 4.6 Collyard et al. 

1994 

Amphipod 

(24-26 days), 

Hyalella azteca

Technical 40 96 hr LC50 4.6 Collyard et al. 

1994 

Crayfish, 

Procambarus 

clarkii

- - 7 days BCF = 4.9 10 Kanazawa 1978 

Stonefly 

(nymph), 

Pteronarcys 

californicus

- - 48 hr EC50 74 Cope 1965a 
Table 6. (continued) 

52 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Caddisfly 

(larva), 

Hydropsyche 

morosa

- - 6 hr LC50 2,500 Fredeen 1972 

Caddisfly 

(larva), 

Hydropsyche 

morosa

- - 6 hr LC50 500 Fredeen 1972 

Caddisfly 

(larva), 

Hydropsyche 

recurvata

- - 6 hr LC50 >500 Freeden 1972 

Caddisfly 

(larva), 

Hydropsyche 

recurvata

- - 6 hr LC50 >500 Freeden 1972 

Mosquito 

(4th instar), 

Aedes aegypti

Technical - 24 hr LC50 350 Klassen et al. 

1965 

Mosquito 

(3rd-4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 61 Chen et al. 1971 

Mosquito 

(3rd-4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 80 Chen et al. 1971 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 3.5 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 5.7 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 2.2 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 3.2 Yasuno and 

Kerdpibule 1967 
Table 6. (continued) 

53 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 4.6 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 4.5 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 1.9 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 1.8 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 5.4 Yasuno and 

Kerdpibule 1967 

Mosquito 

(4th instar), 

Culex pipiens 

fatigans

Technical - 24 hr LC50 3.5 Yasuno and 

Kerdpibule 1967 

Midge 

(1st instar), 

Chironomus 

riparius

Analytical 

(99.7%) 

- 96 hr LC50 (fed) 23 Stuijfzand et al. 

2000 

Midge 

(4th instar), 

Chironomus 

riparius

Analytical 

(99.7%) 

- 96 hr LC50 (fed) 167 Stuijfzand et al. 

2000 

Salmonidae Emulsible 

concentrate 

(60%) 

- 96 hr LC50 8,000 Ciba-Geigy 

1976 

Brown Trout 

(3.22 g), 

Salma trutta 

lacustris

- - 96 hr LC50 602 Swedberg 1973 

Cutthroat trout 

(0.52 g), 

Oncorhynchus 

clarki

- - 96 hr LC50 3,850 Swedberg 1973 
Table 6. (continued) 

54 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Cutthroat trout 

(2.02 g), 

Oncorhynchus 

clarki

- - 96 hr LC50 2,760 Swedberg 1973 

Rainbow trout 

(fry), 

Oncorhynchus 

mykiss

Insecticidal 

soap 

- 96 hr LC50 20 Mitchell 1985 

Rainbow trout, 

Oncorhynchus 

mykiss

- - 48 hr EC50 170 Cope 1965a 

Rainbow trout 

(16 g), 

Oncorhynchus 

mykiss

Synthesized - 14 days BCF = 62 15 Seguchi and 

Asaka 1981 

Rainbow trout, 

Oncorhynchus 

mykiss

Analytical 360 28 days NOEC 200 Bresch 1991 

Goldfish 

(4.01 cm), 

Carassius 

auratus

Technical - 48 hr LC50 5,100 Nishiuchi and 

Hashimoto 

1967; 

Hashimoto and 

Nishiuchi 1981 

Carp, 

Cyprinus carpio

- - 7 days BCF = 65.1 10 Kanazawa 1978 

Carp (4.2 cm), 

Cyprinus carpio

Technical - 72 hr LC50 2,000 Nishiuchi and 

Asano 1981 

Carp (6.0 cm), 

Cyprinus carpio

Technical - 48 hr LC50 3,200 Nishiuchi and 

Hashimoto 

1967; 

Hashimoto and 

Nishiuchi 1981; 

Nishiuchi and 

Asano 1981 

Carp (8 g), 

Cyprinus carpio

Synthesized - 14 days BCF = 120 18 Seguchi and 

Asaka 1981 

Carp (1.1-1.4 g), 

Cyprinus carpio

- - 72 hr LC50 1,420 Dutt and Guha 

1988 

Carp (24-35 g), 

Cyprinus carpio

Reagent 

(98%) 

- 7 days BCF = 20.9 2.4 Tsuda et al. 1990 

Fathead minnow 

(larva), 

Pimephales 

promelas

Technical 

(88.2%) 

44-49 7 days No reduction in 

growth or 

survival 

277 Norberg-King 

1989 
Table 6. (continued) 

55 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Fathead minnow 

(larva), 

Pimephales 

promelas

Technical 

(88.2%) 

44-49 7 days Reduction in dry 

weight 

277 Norberg-King 

1989 

Fathead minnow 

(larva), 

Pimephales 

promelas

Technical 

(88.2%) 

44-49 7 days Reduction in dry 

weight 

347 Norberg-King 

1989 

Fathead minnow 

(embryo-larva), 

Pimephales 

promelas

Technical 

(88.2%) 

44-49 12 days No reduction in 

growth or 

survival 

285 Norberg-King 

1989 

Fathead minnow 

(newly hatched 

larvae), 

Pimephales 

promelas

Encapsulated 

formulation 

(fresh stock) 

45.8 96 hr LC50 6,100 Jarvinen and 

Tanner 1982 

Fathead minnow 

(newly hatched 

larvae), 

Pimephales 

promelas

Encapsulated 

formulation 

(11 week-old 

stock) 

45.8 96 hr LC50 5,100 Jarvinen and 

Tanner 1982 

Fathead minnow 

(embryo-larva), 

Pimephales 

promelas

Encapsulated 

formulation 

45.8 32 days No effect on 

weight 

40 Jarvinen and 

Tanner 1982 

Fathead minnow 

(embryo-larva), 

Pimephales 

promelas

Encapsulated 

formulation 

45.8 32 days Significant 

reduction in 

weight 

76 Jarvinen and 

Tanner 1982 

Catfish 

Ictalurus sp. 

Emulsifiable 

concentrate 

(60%) 

- 96 hr LC50 8,000 Ciba-Geigy 

1976 

Ide 

Leucisuc idus

Emulsifiable 

concentrate 

(60%) 

- 96 hr LC50 150 Ciba-Geigy 

1976 

Flagfish 

(larva-juvenile), 

Jordanella 

floridae

- - 21-day 

pulsed 

dose 

+ recovery 

Decreased egg 

production 

290 Allison 1977 

Flagfish 

(juvenile-adult), 

Jordanella 

floridae

- - 21-day 

pulsed 

dose 

+ recovery 

Decreased 

parental survival 

250 Allison 1977 
Table 6. (continued) 

56 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Flagfish (adultspawning), 

Jordanella 

floridae

- - 21-day 

pulsed 

dose 

+ recovery 

Decreased 

survival of 

parents and larvae 

1,170 Allison 1977 

Oriental 

weatherfish, 

Misqurnus 

anguillicaudatus

Technical - 48 hr LC50 500 Hashimoto and 

Nishiuchi 1981 

Oriental 

weatherfish 

(2.6 g), 

Misgurnus 

anguillicaudatus

Synthesized - 14 days BCF = 28 14 Seguchi and 

Asaka 1981 

Guppy (7 wk), 

Poecilia 

reticulata

Technical - 24 hr LC50 3,700 Chen et al. 1971 

Guppy (7 wk), 

Poecilia 

reticulata

Technical - 24 hr LC50 3,800 Chen et al. 1971 

Guppy (7 wk), 

Poecilia 

reticulata

Technical - 30 min Loss of 

equilibrium 

7,000 Chen et al. 1971 

Guppy, 

Poecilia 

reticulata

Emulsifiable 

concentrate 

(60%) 

- 96 hr LC50 3,000 Ciba-Geigy 

1976 

Guppy, 

Poecilia 

reticulata

- - 7 days BCF = 17.5 10 Kanazawa 1978 

Guppy 

(2-3 mon), 

Poecilia 

reticulata

Technical 

(99%) 

100 3 days Lethal body 

burden 

2,495 Ohayo-Mitoko 

and Deneer 1993 

Guppy 

(2-3 mon), 

Poecilia 

reticulata

- 75 24 hr Lethal body 

burden 

(@ 4,330 μg/L 

exposure) 

2.1 (μmol/g) Deneer et al. 

1999 

Guppy 

(2-3 mon), 

Poecilia 

reticulata

- 75 7 days Lethal body 

burden (@ 2,420 

μg/L exposure) 

1.8 (μmol/g) Deneer et al. 

1999 

Bluegill, 

Lepomis 

macrochirus

- - 48 hr EC50 30 Cope 1965a 
Table 6. (continued) 

57 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Bluegill, 

Lepomis 

macrochirus

Basudin 

 (93%) 

- 48 hr LC50 1,493 Li and Chen 

1981 

Zebrafish, 

Brachydanio 

rerio

ELS Analytical 360 200->200 >200 Bresch 1991 

Tilapia, 

Tilapia sp. 

- - 48 hr LC50 1,492 Li and Chen 

1981 

Mozambique 

tilapia (5-9 g), 

Tilapia 

mossambica

Technical - - LC100 15,850 Mustafa et al. 

1982 

Mozambique 

tilapia 

(3.56 g), 

Tilapia 

mossambica

- - 96 hr LC50 2,280 Chatterjee and 

Konar 1984 

Mozambique 

tilapia (1.4 g), 

Tilapia 

mossambica

- - 72 hr LC50 2,880 Dutt and Guha 

1988 

Experimental 

stream 

community 

Technical 

(92.5%) 

170-195 84 days Increased drift 

rates for Hyalella

0.3 Arthur et al. 

1983 

Experimental 

stream 

community 

Technical 

(92.5%) 

170-195 112 days Reduced Hyalella

populations 

5 Arthur et al. 

1983 

Experimental 

pond community 

Technical 

(88%) 

70-150 70 days NOEC for 

phytoplankton 

and periphyton 

chlorophyll; 

macrophyte 

biomass 

443 Giddings et al. 

1996 

Experimental 

pond community 

Technical 

(88%) 

70-150 70 days LOEC for 

Cladocera, 

Pentaneurcini, 

Ceratopogonidae 

abundance 

2.4 Giddings et al. 

1996 

Experimental 

pond community 

Technical 

(88%) 

70-150 70 days LOEC for 

zooplankton and 

macroinvertebrate 

taxonomic 

richness 

9.2 Giddings et al. 

1996 

Experimental 

pond community 

Technical 

(88%) 

70-150 70 days Reduced bluegill 

sunfish biomass 

22 Giddings et al. 

1996 
Table 6. (continued) 

58 

Species Chemicala

Hardness 

(mg/L as 

 CaCO3) Duration Effect

Concentration 

 (μg/L)__ Reference

Experimental 

pond community 

Technical 

(88%) 

70-150 70 days Reduced bluegill 

sunfish survival 

54 Giddings et al. 

1996 

Species Chemicala

Salinity 

 (g/kg) Duration Effect

Concentration

(μg/L) Reference

SALTWATER SPECIES

Natural 

phytoplankton 

- - 4 hr 6.8% decrease in 

photosynthesis 

1,000 Butler 1963 

Red alga, 

Champia 

parvula

(96%) - 48 hr 

exposure 

No effect on 

sexual 

reproduction 

1,000 Thursby & 

Tagliabue 1988 

Red alga, 

Chondrus 

crispus

(12.5%) - 24 hr 

exposure 

18 day 

holding 

No effect on 

growth 

10,000 Shacklock & 

Croft 1981 

Rotifer, 

Brachionus 

plicatilis

(96%) - 24 hr LC50 55,100 Thursby & Berry 

1988 

Rotifer, 

Brachionus 

plicatilis

Standard 

(95%) 

- 24 hr EC50 28,000 Guzzella et al. 

1997 

Snail, 

Lacuna vincta

(12.5%) - 3 hr 

exposure, 

48 hr 

holding 

88% mortality 1,000 Shacklock & 

Croft 1981 

Snail, 

Lacuna vincta

(12.5%) - 3 hr 

exposure, 

48 hr 

holding 

75% mortality 10,000 Shacklock & 

Croft 1981 

Eastern oyster, 

Crassostrea 

virginica

- - 96 hr No decrease in 

shell growth 

1,000 Butler 1963; 

Mayer 1987 

Eastern oyster 

(5-10 cm 

height), 

Crassostrea 

virginica

Technical 

and 14Clabeled 

- 96 hr LC50 shell 

growth 

1,115 Williams 1989 

Eastern oyster 

(6-10 cm 

height), 

Crassostrea 

virginica

Technical 

and 14Clabeled 

- 5 days BCF = 56 100 Williams 1989 
Table 6. (continued) 

59 

Species Chemicala

Salinity 

 (g/kg) Duration Effect

Concentration

(μg/L) Reference

Amphipod 

(adult), 

Ampelisea aldita

Technical 25 48 hr LC50 10 Werner & Nagel 

1997 

Amphipod, 

Gammarus 

oceanicus

(12.5%) - 3 hr 

exposure 

100% mortality 1,000 Shacklock & 

Croft 1981 

Amphipod 

(adult), 

Rhepoxynius 

abronius

Technical 31 24 hr LC50 9.2 Werner & Nagel 

1997 

Isopod, 

Idotea baltica

(12.5%) - 3 hr 

exposure 

100% mortality 1,000 Shacklock & 

Croft 1981 

Brown shrimp, 

Penaeus aztecus

- - 24 hr EC50 44 Butler 1963 

Brown shrimp, 

Penaeus aztecus

Technical 

95.1% pure 

- 48 hr EC50 28 Mayer 1987 

Grass shrimp, 

Palaemonetes 

pugio

Technical 

 95.1% pure 

- 48 hr EC50 28 Mayer 1987 

White mullet, 

Mugil curema

- - 24 & 48 hr LC50 250 Butler 1963 

Striped mullet, 

Mugil cephalus

Technical 

 95.1% pure 

- 48 hr LC50 150 Mayer 1987 

Sheepshead 

minnow, 

Cyprinodon 

variegatus

92.6% pure - 108 days Decrease in 

acetylcholinesterase activity 

0.47 Goodman et al. 

1979; Mayer 

1987 

a

 Percent purity is listed in parentheses when available. 
60 

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