Bioconcentration kinetics of hydrophobic chemicals in different densities of Chlorella pyrenoidosa

Abstract

Algal density‐dependent bioconcentration factors and rate constants were determined for a series of hydrophobic compounds in Chlorella pyrenoidosa. The apparent uptake rate constants of the hydrophobic compounds in algae varied between 200 and 710,000 L/kg/d, slightly increased with hydrophobicity within an experiment, were relatively constant for each algal density, and fitted fairly within existing allometric relationships. The bioavailability of the hydrophobic test compounds was significantly reduced by sorption by algal exudates. The sorption coefficients of the hydrophobic compounds to the algal exudates were between 80 and 1,200 L/kg, and were for most algal densities in the same order of magnitude as the apparent bioconcentration factors to the algae, that is, between 80 and 60,200 L/kg. In typical field situations, however, no significant reduction in bioavailability due to exudates is expected. The apparent elimination rate constants of the hydrophobic compounds were high and fairly constant for each algal density and varied between 2 and 190/d. Because the apparent elimination rate constants were higher than the growth rate constant, and were independent of hydrophobicity, we speculated that other factors dominate excretion, such as exudate excretion‐enhanced elimination. Bioconcentration factors increased less than proportional with hydrophobicity, i.e., the octanol–water partition coefficient [Kow]. The role of algal composition in bioconcentration is evaluated. Bioconcentrations (kinetics) of hydrophobic compounds that are determined at high algal densities should be applied with caution to field situations.

Unraveling the Relationship between the Concentrations of Hydrophobic Organic Contaminants in Freshwater Fish of Different Trophic Levels and Water Using Passive Sampling

“…Implications. The C L value in fishes of TL < 4 being lower than C L⇌water is not compatible with the general belief that trophic magnification typically amplifies the levels of persistent HOCs in, for example, fish above that of the surrounding Modeled time required for algae to attain the concentration within 10% equilibrium (t 90 ) for three cases where ∼25 × 10 −6 kg algae was exposed to (I) 0.05 L, 40 (II) 1 L, 42 or (III) infinite volume of water, plotted versus log BCF with the y-axis at a logarithmic scale (panel A) and at a linear scale for 0−50 days (panel B). Solid and dashed lines indicate t 90 for the algal uptake and water phase decrease, respectively.…”

“…Using these models, C A t and C W t were modeled as a function of time for three cases involving HOC uptake by the same algal mass (∼25 × 10 −6 kg): (I) V W = 0.05 L and A A = 10 dm 2 by Sijm et al, 40 (II) V W = 1 L and A A = 16 dm 2 by Koelmans et al, 42 and (III) V W = ∞ (field situation) and A A = 10 dm 2 , assuming a hypothetical situation that algae do not grow (see S21-1 for more detail). An average k W of 0.1 μm s −1 (0.09 dm d −1 ) was derived by fitting k e to the rate constants reported for the cases (I) 40 and (II). 42 This k W was used in all three cases, providing sampling rates (R S = k W A A ) of 0.86, 1.35, and 0.86 L d −1 for (I), (II), and (III), respectively.…”

“…This is because for equilibration in a defined water volume with m A BCF/V W ≫ 1, t A 90 is determined byV W , rather than BCF. 40 For the aqueous phase, the profiles in panel A of Figure when m A BCF/V W = 1, and for higher ratios, the relative difference between t W 90 and t A 90 is determined by the phase capacity factor log(m A BCF/V W ), by which C W has to decrease to attain a level within 10% from equilibrium i k j j j j j y { z z z z z i k j j j j j y { z z z z z…”

“…Figure 4. Modeled time required for algae to attain the concentration within 10% equilibrium (t 90 ) for three cases where ∼25 × 10 −6 kg algae was exposed to (I) 0.05 L,40 (II) 1 L,42 or (III) infinite volume of water, plotted versus log BCF with the y-axis at a logarithmic scale (panel A) and at a linear scale for 0−50 days (panel B). Solid and dashed lines indicate t 90 for the algal uptake and water phase decrease, respectively.…”

Mathematical Modeling of Microalgal Internal Metabolic Behaviors under Heterotrophic Conditions and Its Application

“…(Obliquus). ,− Note that unmeasured substrates in the collected data sets are assumed to be available sufficiently. Minimum and maximum quotas of the internal components are determined on the basis of the experimental results in the previous studies, e.g., the weight of a single cell ,− and weight fractions of the internal components . In this way, 24 parameters become fixed, and the rest of the parameters are decided by minimizing the objective function represented in eq .…”