John q
Member
I honestly don't know mate. Personally I'd be reluctant to dose any levels simply because there's mixed information out there as to the toxity of Salicylic acid/Acetylsalicylic and fish.This means it is safe to dose one baby aspirin or 89 gm daily to carp, and probably also OK to dose full strength or 350 gm non daily.
I think there definitely needs to be some hobbyist type experiments done to work out if a sweet spot can be found that kills off algae and has no negative effects on plants, I just think this should be done initially without potentially harming our livestock.
On a related note I found this information that suggests in not to high doses salicylic acid can also be harmful to plants.
Any other information on results incl. tables
At 60 and 120 mg/l of salicylic acid reduced the final leaf number, the dry weight and the chlorophyll contents of L. minor (see table 1 below).Chlorophyll contents in Lemna tissues and in water are negatively correlated.
The highest dose caused a rapid yellowing of leaves.
Table 1: Effect of salicylic acid on the growth, biomass and chlorophyll contents of L. minor. Values expressed as percentage of controls after 7 days exposure.
Nominal concentration of salicylic acid (mg/L) | No. of leaves | biomass (dry weight) | Chlorophyll content | |
Tissue | water | |||
15 | 94* | 100 | 102 | 160 |
30 | 96 | 90 | 100 | 180 |
60 | 90* | 75* | 75* | 220* |
120 | 20* | 15* | 3* | |
* data significantly different from controls.
It was suggested in the article that additional toxic effect on the plants are likely at a pH below 5.
table 2 : pH values at different concentrations in salicylic acid and sodium salicylate
concentration in mg/L | 0 | 15 | 30 | 60 | 120 |
pH in salicylic acid solution | 6.74 | 6.60 | 6.42 | 5.92 | 3.66 |
pH in sodium salicylate solution | 6.89 | 6.92 | 7.00 | 7.14 | 7.38 |
Applicant's summary and conclusion
Validity criteria fulfilled:not specifiedRemarks:not applicable no guideline followed and not enough data to assess validity criteriaConclusions:In the conditions tested, salicylic acid showed a slight effect on growth of the aquatic plant Lemna minor.However, complementary results with sodium salicylate which does not lower the pH as much as salicylic acid showed no toxicity directly linked to the substance. This toxicity of salicylic acid therefore might be due to a physical effect (acid).Executive summary:
In a 7 days acute toxicity test, single-leaf plants of Lemna minor were exposed to salicylic acid at nominal concentrations of 0, 15, 30, 60 and 120 mg/L.
The study did not followed a guideline but seems to be scientifically well performed.
Growth inhibition was recorded via biopmass parameters (dry weight, number of leaves and chlorophyll content inside tissues and in water).
These parameters and were significantly different from control between 60 and 120 mg/L, therefore the The 7 -d EC50 is between 60 and 120 mg/L of salicylic acid.
Yellowing was only observed at the highest concentration tested.
In the test conditions, salicylic acid is considered as harmful to algae according to Directive 67/548/EEC criteria.
Authors also indicate that salicylic acid and sodium salicylate are of a lower toxicity to aquatic plants in a concentration range up to 50 mg per liter and could be ranked into class 1 of chemicals with a low hazard potential (Geyer et al., 1985).
Considering the effect on solution pH of salicylic acid it is therefore relevant to consider that the toxic effect observed in this study is related to a physical effect (acid) and as suggested by authors, to consider salicylic acid as a substance with low hazard potential.
The authors have not followed any guideline and no information is given for GLP, analytical monitoring of the substance, purity of the substance, test conditions. But, it seems that the method mainly follows OECD guidelines with deviations (no reference substances testing, four concentrations tested). And analysis of the results is reliable by considering the potential pH effect on the toxicity.
Therefore this toxicity study is considered as reliable with restrictions.