A few studies have used Tenax to evaluate the bioavailability of pyrethroids
[25–27]. Pyrethroids were found not to be very bioavailable to sediment-dwelling
organisms such as Lumbriculus variegatus and to have a low toxicity to Hyalella
azteca. Additionally, ageing time showed no significant influence on bioavailability;
for instance, desorption decreased quickly over contact time meaning bioavailability
diminished accordingly. However, these studies were mostly limited to chemical
analyses. Combining Tenax desorption kinetics with toxicity response could shed
a light on the pyrethroid fraction that is bioavailable and can affect the organisms
[25, 28]. The toxicity of sampled sediments appears to be better predicted when
confronted with measured residue levels from Tenax extracts [25].
A different study evaluated the bioavailability of pyrethroids in sediments with
different organic carbon contents using Tenax extractions [29]. Toxicity experiments
were performed using Daphnia magna, which is extremely sensitive to λ-cyhalothrin
and deltamethrin, as a surrogate sediment toxicity test organism [30, 31]. As a
planktonic organism that lives on the water column, Daphnia magna is exposed to
the bioavailable pyrethroid fraction in the water phase rather than the fraction bound
to sediment particles.
Two sediment samples free of pyrethroids were collected along the Ebro River
(north-east of Spain) far away from agricultural, industrial and highly urbanized
areas, and toxicity experiments were performed on sediment from a pristine water
reservoir located in Huesca (north-east of Spain) with no sources of pollution [29].
Rapid desorption took place in the first 30 h of desorption, while slow desorption
was observed from hour 72 to 432. The slow desorption would represent the
fraction of contaminant that is strongly bound to the sediment’s organic matter.
Bioavailability increased with the decrease in organic carbon content, which had
previously been reported for cypermethrin [32]. The percentage of desorption
was 10–20% for sediment I (5.8% of organic content) and 15–40% for sediment II
(2% of organic content). The percentages of desorption were ranged between
4 and 17% for cyfluthrin, cypermethrin, fluvalinate and phenothrin in sediment I
and between 7 and 36% in sediment II [29]. Furthermore, the kinetic constant
for the first 6 h of desorption was also greater for sediment II. Conversely, the
desorptions of bifenthrin, λ-cyhalothrin and deltamethrin were very similar for
both sediments, 3–22%.
Coincidentally, cyfluthrin, with the second highest log K ow of the selected
pyrethroids, was observed to be the most bioavailable compound, while λ-cyhalothrin,
with the lowest log K ow , was the less bioavailable of the assessed pyrethroids [29].
However, this correlation was not observed for the rest of the pyrethroids. The order
of the other pyrethroids was not the same in both sediments, but cypermethrin,
esfenvalerate and permethrin were always in the most bioavailable half, fenpropathrin
and fluvalinate were around the centre of the list, and bifenthrin and tetramethrin
were in the less bioavailable half.
Another publication reported that the Tenax method is better than using solidphase microextraction fibres because of its capacity to remove a larger fraction of
the contaminant from the matrix [33]. Their calculated percentages of desorption
were greater than those listed above as the organic carbon content of the sediment
was lower.
208
Ò. Aznar-Alemany and E. Eljarrat
[25–27]. Pyrethroids were found not to be very bioavailable to sediment-dwelling
organisms such as Lumbriculus variegatus and to have a low toxicity to Hyalella
azteca. Additionally, ageing time showed no significant influence on bioavailability;
for instance, desorption decreased quickly over contact time meaning bioavailability
diminished accordingly. However, these studies were mostly limited to chemical
analyses. Combining Tenax desorption kinetics with toxicity response could shed
a light on the pyrethroid fraction that is bioavailable and can affect the organisms
[25, 28]. The toxicity of sampled sediments appears to be better predicted when
confronted with measured residue levels from Tenax extracts [25].
A different study evaluated the bioavailability of pyrethroids in sediments with
different organic carbon contents using Tenax extractions [29]. Toxicity experiments
were performed using Daphnia magna, which is extremely sensitive to λ-cyhalothrin
and deltamethrin, as a surrogate sediment toxicity test organism [30, 31]. As a
planktonic organism that lives on the water column, Daphnia magna is exposed to
the bioavailable pyrethroid fraction in the water phase rather than the fraction bound
to sediment particles.
Two sediment samples free of pyrethroids were collected along the Ebro River
(north-east of Spain) far away from agricultural, industrial and highly urbanized
areas, and toxicity experiments were performed on sediment from a pristine water
reservoir located in Huesca (north-east of Spain) with no sources of pollution [29].
Rapid desorption took place in the first 30 h of desorption, while slow desorption
was observed from hour 72 to 432. The slow desorption would represent the
fraction of contaminant that is strongly bound to the sediment’s organic matter.
Bioavailability increased with the decrease in organic carbon content, which had
previously been reported for cypermethrin [32]. The percentage of desorption
was 10–20% for sediment I (5.8% of organic content) and 15–40% for sediment II
(2% of organic content). The percentages of desorption were ranged between
4 and 17% for cyfluthrin, cypermethrin, fluvalinate and phenothrin in sediment I
and between 7 and 36% in sediment II [29]. Furthermore, the kinetic constant
for the first 6 h of desorption was also greater for sediment II. Conversely, the
desorptions of bifenthrin, λ-cyhalothrin and deltamethrin were very similar for
both sediments, 3–22%.
Coincidentally, cyfluthrin, with the second highest log K ow of the selected
pyrethroids, was observed to be the most bioavailable compound, while λ-cyhalothrin,
with the lowest log K ow , was the less bioavailable of the assessed pyrethroids [29].
However, this correlation was not observed for the rest of the pyrethroids. The order
of the other pyrethroids was not the same in both sediments, but cypermethrin,
esfenvalerate and permethrin were always in the most bioavailable half, fenpropathrin
and fluvalinate were around the centre of the list, and bifenthrin and tetramethrin
were in the less bioavailable half.
Another publication reported that the Tenax method is better than using solidphase microextraction fibres because of its capacity to remove a larger fraction of
the contaminant from the matrix [33]. Their calculated percentages of desorption
were greater than those listed above as the organic carbon content of the sediment
was lower.
208
Ò. Aznar-Alemany and E. Eljarrat