Effect of pH on the toxicity and bioconcentration of sulfadiazine on Daphnia magna.

The antimicrobial sulfonamide sulfadiazine has in the last decades been detected in environmental water bodies, both surface and ground water. Since pH in the environment may vary considerably, this study examined the toxicity of the amphoter sulfadiazine towards Daphnia magna at pH levels of 6.0, 7.5 and 8.5, thus taking the impact of speciation into consideration, contrary to earlier eco-toxicity studies conducted at standard conditions. Toxicity tests were performed using the standard ISO 6341 test procedure modified to accommodate the three pH levels and the toxicity was expressed as EC50. After 48 h the EC50 was determined to be 27.2, 188 and 310 mg L(-1) at pH 6.0, 7.5 and 8.5, respectively, thus demonstrating a significant effect of pH on the toxicity of sulfadiazine. Furthermore, the bioconcentration factor (dry weight) was determined to be 50 and 36 at pH 6.0 and 8.5, respectively. The higher toxicity at the lower pHs was assumed to be caused by the higher fraction of un-ionized sulfadiazine at the lower pHs. However, the one and a half fold higher bioconcentration at pH 6.0 relative to pH 8.5 does not match the more than ten times higher toxicity at pH 6.0. When comparing the fraction of neutral compound to toxicity and bioconcentration results neither toxicity nor bioconcentration can be ascribed solely to the unionized fraction of sulfadiazine.

Dichlobenil and 2,6-dichlorobenzamide (BAM) in the environment: what are the risks to humans and biota?

Dichlobenil is a herbicide widely used for weed control, mainly in non-agricultural areas and in the aquatic environment. When released into the environment, dichlobenil can undergo many processes such as vaporization to air, binding to soil and sediment, as well as degradation to a number of new compounds. The main metabolite is 2,6-dichlorobenzamide (BAM) which is water soluble and causes ground water contamination. It is frequently found in levels exceeding maximum allowed concentrations of pesticides and metabolites in ground water (0.1 µg/L) set by the European Commission. The environmental distribution of both dichlobenil and BAM was outlined and the risk quotients were calculated for biota and for humans. For organisms living in aquatic habitats, risk quotients were low for both dichlobenil and BAM, approximately 0.02 for dichlobenil and 2.4·10(-4) to 1.3·10(-3) for BAM. For humans, a margin of safety above 15,000 was estimated for dichlobenil. The most unusual and extreme concentration of BAM ever found in ground water is 560 µg/L. Even at this concentration, the margin of safety for humans was 313 for a 70 kilo man and 56 for a 25 kilo child. The results clearly demonstrate that the risks to biota and humans are very low.

Analysis and environmental concentrations of the herbicide dichlobenil and its main metabolite 2,6-dichlorobenzamide (BAM): a review.

Dichlobenil is an herbicide which has been applied in many countries for weed control in non-agricultural areas such as railroads, car parks and private gardens. In the aquatic environment it has been used for control of floating aquatic weeds. Dichlobenil is relatively persistent in the environment, and primarily bound to solid matrices. Of great concern is its main degradation product 2,6-dichlorobenzamide which is water soluble and therefore transported downward in aquifers, contaminating groundwater resources. It is often found in concentrations exceeding 0.1 µg/L, which is the maximum allowed concentration of pesticides in groundwater set by the European Commission. In many countries, the usage of dichlobenil and the problems associated with groundwater contamination by 2,6-dichlorobenzamide have resulted in intensive research and monitoring of these compounds. This review gives the first overview of analytical strategies available for determining dichlobenil and 2,6-dichlorobenzamide in environmental matrices. It also summarizes studies presenting measured environmental concentrations of dichlobenil and 2,6-dichlorobenzamide identified in the literature during the past two decades. Thereby a preliminary picture of the distribution of dichlobenil and 2,6-dichlorobenzamide in the environment can be outlined for the first time.