結論は、このバジルを1週間に100g食べても、そこから予測されるアトラジンの摂取量0.744μg/kg bw/day はARfD の0.74%に過ぎないのでリスクはほとんどないというのが私の意見です。
ADI (mg/kg bw/day) of atrazine: Japan 0.004, JMPR 0.02, USEPA 0.0018, EU- no registration
ARfD (mg/kg bw/day) of atrazine: JMPR 0.1, USEPA 0.1
MRL (ppm=mg/kg basil) of atrazine in Japan: leaves and stems (grouped as other herbs) 0.02ppm, seeds (grouped as other spices) 0.06ppm
MRL is so set as to keep the total MRL of each crop below the ADI. Although the atrazine residue detected in Thailand 2.6mg/kg basil (=2ppm) obviousely exceeds the MRL in Japan, it is not proper for me to assess the risk without information on the food factor and MRLs of atrazine for other crops in Thailand. For MRL of a pesticide on different crops can be greatly different among countries.
So, I would suggest you to assess the risk by comparing the expected intake of atrazine consuming the basil with either the ADI or ARfD (preferable) of atrazine.
If you consume 100g of basil per week in Thailand and average bw (body weight) of Thai people is 50kg, you might consume
100g of basil/50kg bw/7 days
14.3g of basil/50kg bw/day
0.286g (=286mg) of basil/kg bw/day
Since atrazine detected was 2.6mg/kg basil, atrazine you might intake from the basil would be
2.6mg atrazine/kg (=1,000g) basil
37.2μg atrazine/14.3g basil
0.744μg atrazine/0.286g basil
0.744μg atrazine/kg bw/day (expected intake)
The 0.744μg atrazine/kg bw/day is less than any of the three ADIs given above, accounting for 18.6%, 3.7%, and 41.3%, respectively, of the ADIs Japan, JMPR, and USEPA.
However, a comparison of the expected intake of atrazine with the ADIs may result in an over-estimation of risk. Because (a) the residue 2.6mg/kg basil was found only in one out of eight (or was it eighteen?) samples analyzed and considered to be rather exceptional, (b) the ADI is a safety measure for consuming the basil continuousely for a life-long period, and it is quite unlikely that Thai people would keep eating the basil with the current level of atrazine residue everyday for a life-long period.
More rational approach is to compare the 0.774μg atrazine/kg bw/day with the ARfD of atrazine 0.1 mg(=100μg)/kg bw/day. The expected intake of atrazine by consuming the basil is far less than the ARfD of JMPR and USEPA accounting for only 0.74% of the ARfD.
Therefore, I believe eating the basil with the atrazine residue at 2.6mg/kg level will pose little, if any, risk to Thai consumers and it is well within the acceptible range.
If I were in charge of pesticide regulation in Thailand, though, I would be interested in knowing where the one out of eight samples of basil with the atrazine residue was grown and under which condition to make sure growers are observing the use pattern of the herbicide correctly.