APPENDIX M. RE-ANALYSIS OF ATRAZINE TOXICITY DATA USED FOR 

CONSTRUCTING PATI 

(3 Pages) 

NOTES FOR MARCH 28-30, 2012,

These notes describe the corrections and changes to the toxicity data for constructing the PATI 

relationship that were made between the finalization of Appendix E and the more recent Table 

19 in the white paper. 

(1) All regression analyses used for slopes and EC50s in original toxicity parameter database 

were redone with all three TRAP models instead of just logistic model. For the logistic analysis, 

this provided the same results within convergence variation with the following exceptions: 

(a) Hinman 1989 Hydrilla – original analysis used the sigmoidal threshold model 

(b) Zagorc-Koncan 1996 Scenedesmus – original analysis used the sigmoidal threshold model 

(c) Hoberg 1993c Lemna – original analysis (and report) had final concs rather than average 

(d) Roberts 1990 Selenastrum – original analysis had an error in one SGR 

(2) In addition to correcting the above mistakes in the original analysis for the final compilation, 

it was noted that the report had a few errors that needed to be corrected in redoing the analyses. 

(a) Fairchild et al. 1994 Najas – report has concentration 8.4 – should be 9.4 

(b) Fairchild et al. 1994 Lemna – multiple errors in SGR in the report – corrected to original 

(c) Hinman 1989 Hydrilla – slope in report table differs from that in analysis in appendix 

(d) Forney and Davis 1981 – slope in report table differs from that in analysis in appendix 

(3) Slopes for all three models were log-transformed and compiled for determination of mean 

and standard deviation in Statistica. 

Original log slopes – mean = -0.058, stdv = 0.180 

New log slopes – mean = -0.071, stdv = 0.195 (Logistic Model) Range 0.54,0.85,1.33 

 – mean = -0.059, stdv = 0.191 (Threshold Model) Range 0.56,0.87,1.36 

 – mean = -0.163, stdv = 0.186 (Piecewise Model) Range 0.45,0.69,1.05 

(4) Author-reported EC50s for SGR surrogates that were used unchanged in the original analysis 

were used for the compilation for all three models these included: 

Versteeg 1990 Selenastrum 

Turbak et al. 1986 Selenastrum 

Hersh and Crumpton 1989 Chlamydomonas, Chlorella 

Stratton 1981, 1984 Anabaena sp, Chlorella, Scenedesmus 
(5) Kallqvist and Romstad 1994 reported an EC10 of 27 and an EC50 of 110 for the SGR and 

this was converted to a slope for each model as follows: 

Logistic: ܵ ൌ

୪୬ ሺ ೛

భష೛ሻ

ସሺ୪୭୥ሺா஼௣ሻି୪୭୥ሺா஼ହ଴ሻሻ ൌ 0.900

ܵ ൌ ଵିඥଶ௣ Threshold: ୪୭୥ሺா஼ହ଴ሻି୪୭୥ ሺா஼௣ሻ ൌ 0.906

ܵ ൌ ௣ି଴.ହ

୪୭୥ሺா஼௣ሻି୪୭୥ሺா஼ହ଴ሻ Piecewise: ൌ 0.656 

 (6) For Schafer et al 1993, the EC50 of 51 corresponded to an 16.0% reduction in the SGR if 

this EC50 was for biomass increase and a 19.6% reduction in the SGR if this EC50 was for 

AUC, given an SGRC=1.06/d. This was extrapolated to an EC50 for the SGR using all three 

models and using the low, med, high steepness from analyses of just algae data: 

Algae log slopes – mean = -0.054, stdv = 0.147 (Logistic Model) Range 0.63,0.88,1.24 

 – mean = -0.041, stdv = 0.146 (Threshold Model) Range 0.65,0.91,1.27 

 – mean = -0.155, stdv = 0.146 (Piecewise Model) Range 0.50,0.70,0.98 

Because lower/upper bounds were within a factor of 2, estimates for the middle slope were used. 

This resulted in EC50s (assuming biomass vs AUC) of 128.2 vs 150.8, 131.2 vs 153.0, and 138.5 

vs 156.0 for the logistic, threshold, and piecewise models, respectively. The mean of the 

biomass versus AUC were used. 

(7) For Larsen et al. 1986, calculations outlined in the report were repeated for both models and 

with the updated algal steepness in point(6), resulting in update SGR EC50s as follows: 

Test Species 14C EC50

(μg/L) 

SGR EC50

Logistic 

SGR EC50

Threshold 

SGR EC50

Piecewise 

Selenastrum capricornutum 43 81 83 90 

Ankistrodesmus sp. 66 124 127 138 

Chlamydomonas reinhardi 37 70 71 78 

Scenedesmus obliquus 48 90 92 101 

Chlorella vulgaris 308 580 592 645 

Stigeoclonium tenue 175 330 336 367 

Ulothrix subconstricta 88 166 169 184 

Anabaena cylindrica 204 292 294 317 

(8) Kirby and Sheehan 1994 reported similar 10-day Lemna EC50s of 56, 60, and 62 for frond 

number, weight increase, and chlorophyll. Based on the average SGRC for Lemna, the frond 

EC50 was equated to a ECp for SGR and then to an EC50 for SGR using the range of steepness 

for Lemna. 

Lemna log slopes – mean = 0.115, stdv = 0.069 (Logistic Model) Range 1.01,1.30,1.53 

 – mean = 0.124, stdv = 0.055 (Threshold Model) Range 1.17,1.33,1.51 

 – mean = 0.014, stdv = 0.043 (Piecewise Model) Range 0.93,1.03,1.14 
(9) Calculated mean and stdv for logEC50 for new compilation – overall for all tests 

Original log EC50s – mean = 2.123, stdv = 0.366 

New log EC50s – mean = 2.127, stdv = 0.365 (Logistic Model) 

 – mean = 2.133, stdv = 0.366 (Threshold Model) 

 – mean = 2.145, stdv = 0.366 (Piecewise Model)