Time dependence of phase distribution of pyrethroid insecticides in sediment

Abstract

Synthetic pyrethroids are strongly hydrophobic compounds, and their toxicity in sediment is regulated by phase distribution among the sediment, dissolved organic matter, and water phases. In the present study, we spiked and equilibrated four pyrethroids in two sediments, and we characterized their phase distribution as a function of contact time. The freely dissolved concentration measured by solid-phase microextraction was only a small fraction (<16.3%) of the total pore-water concentration as determined by liquid-liquid extraction. The fraction of the freely dissolved concentration was significantly greater in the freshwater sediment (1.7-16.3%) than in the marine sediment (1.1-4.2%) following 9 d of equilibration, and it decreased substantially with contact time to less than 5% at 30 d after sediment dosing. Consequently, the apparent organic carbon partition coefficient (Koc) and dissolved organic carbon partition coefficient (Kdoc) values increased significantly over the contact time, especially in the freshwater sediment, suggesting that phase distribution was not at equilibrium after 9 d of equilibration. If only the freely dissolved concentration is bioavailable, these observations suggest that contact time after sediment dosing may greatly affect the bioavailability and, hence, the toxicity of pyrethroids. Therefore, a long contact time (> or = 30 d) is recommended for sediment toxicity testing of this class of compounds. The dependence of bioavailability on contact time also implies that test conditions must be standardized to allow comparison between laboratory-dosed samples and field samples.

Esfenvalerate toxicity to the cladoceran Ceriodaphnia dubia in the presence of green algae, Pseudokirchneriella subcapitata

“…Previous research has shown that contaminants in an ambient water sample are distributed into three distinct phases: solid adsorbed, dissolved organic carbon adsorbed, and freely dissolved (Liu et al 2004). The freely dissolved fraction of most hydrophobic contaminants ranges from 1 to 27 %, and typically this number decreases over time (Liu et al 2004;Bondarenko et al 2006). In our study we estimated the dissolved esfenvalerate fraction to range from 0.4 to 22.7 % after only 12 h, decreasing with increasing algal concentration, which is consistent with previous findings (Liu et al 2004).…”

Analysis, occurrence, and toxic potential of pyrethroids, and fipronil in sediments from an urban estuary

“…The spatial pattern of fipronil contamination also coincided with pyrethroids, with the highest P FIP occurring at correlated with sediment fines (R s ¼ 0.79; p < 0.01; n ¼ 12), but was not correlated with TOC (R s ¼ 0.31; p < 0.2; n ¼ 18). In the absence of usage data to assess occurrence and persistence, the lower hydrophobicity and sediment-water partition coefficients for fipronil and its degradates compared with pyrethroids [32][33][34] can explain these trends.…”

A GIS model-based screening of potential contamination of soil and water by pyrethroids in Europe

“…Pyrethroids have high affinity for organic carbon and very low solubility in water and volatility to the atmosphere, which makes them less environmentally mobile and harmful pesticides (Brady et al, 2006), although Werner et al (2004), have noticed that they may be highly toxic to fish larvae. Their distribution in the water column is mainly to the sediment compartment and dissolved organic carbon (Spurlock et al, 2005), although the time dependence of phase distribution is an important factor (Bondarenko et al, 2006). Yang et al (2006), observe a significant impact of suspended sediments on the bioavailability of pyrethroids in the water column.…”