Plants bioconcentration factors

The transfer of PBBs from soil to plants is so low, e.g., Table III and References (6,29), that the only important issue In the agricultural scenario appears to be soli ingestion (and possibly ingestion of groundwater) by cattle. Based on an estimated half-life, tj/2> in beef of 120 days (30) an estimated mass of fat per animal, M, of 67 kg and a soil Ingestion rate, Mg, of 0.72 kg/day (31), a reasonably conservative soll-to-fat bioconcentration factor can be obtained ... 

Silver is a normal trace constituent of many organisms (Smith and Carson 1977). In terrestrial plants, silver concentrations are usually less than 1.0 mg/kg ash weight (equivalent to less than 0.1 mg/kg DW) and are higher in trees, shrubs, and other plants near regions of silver mining. Seeds, nuts, and fruits usually contain higher silver concentrations than other plant parts (USEPA 1980). Silver accumulations in marine algae (max. 14.1 mg/kg DW) are due mainly to adsorption rather than uptake bioconcentration factors of 13,000 to 66,000 are not uncommon (USPHS 1990 Ratte 1999). 

A bioconcentration factor (BCF) relates the concentration of a chemical in plants or animals to the concentration of that chemical in the medium in which they live. A BCF of about 7 was calculated for 2-hexanone (Lande et al. 1976) using the empirical regression of Neely et al. (1974). This low BCF indicates that bioconcentration is probably not an important fate mechanism for 2-hexanone released into the environment. Biomagnification of 2-hexanone is also not expected to occur to any great extent (Lande et al. 1976). However, no experimental data on the biomagnification potential of 2-hexanone were located to corroborate these assumptions. 

Food Chain Bioaccumulation. Bioconcentration factors have been determined for algae, shellfish, and fish and exhibit a wide range (29-17,000) (ERA 1976 Oliver and Niimi 1983 Pearson and McConnell 1975). This wide range may be explained in part by species differences in metabolism or differences in concentrations tested. Studies also indicate that hexachlorobutadiene preferentially accumulates in the livers of fish. Further studies which might explain the wide range of BCF values would be helpful. No information was located regarding the bioaccumulation of hexachlorobutadiene in plants or aquatic organisms. More information is needed to determine the importance of terrestrial/aquatic food chain bioaccumulation as a potential human exposure pathway. 

Tam et al. (1996) investigated the uptake from water of a series of chlorinated benzenes by various tissues (leaves, petals, stems, roots) of the soybean plant. For two of the seven compounds investigated, they obtained the following apparent equilibrium leaf-water (BAFi]eafv,) and root-water (BAFimom) bioaccumulation factors (or bioconcentration factors since uptake is only from water, see Fig. 10.5) ... 

Basagran has a herbicidal activity but a high bioconcentration factor (Kinkennon, 1995). Diquat is able to undergo natural photochemical decomposition after application to plant surfaces. Studies show that 50 mg of herbicide is depleted to below 6 mg/kg within 7 days after treatment. In soil, diquat is biodegraded at a rate of 10% per year. In aqueous environments, diquat was degraded to levels that were undetectable in less than 30 days. 

Bioconcentration of organic compounds by aquatic plants has received relatively little research attention. Curves showing uptake and loss of radioactivity by duckweed plants exposed to labelled compounds in axenic cultures are shown in Fig. 2. Rate constants and calculated equilibrium bioconcentration factors are shown in Table III. By comparison with fish data shown in Table I, the plants concentrated fenitrothion and fluorene rather poorly, and aminocarb surprisingly well. Lockhart et al. (14) presented a regression equation based on data from uptake curves ... 

Predicted bioconcentration factors using this equation are also shown in Table IV, and these are generally higher than predictions derived with duckweed plants. 

Table III. Bioconcentration factors vBCF) for Lemna plants in laboratory exposures to several pesticides and a hydrocarbon.

Table IV. Comparison of three estimates of bioconcentration factors for aquatic plants in laboratory tests. Values for duckweed were calculated from the rate constants shown in Table III, and from the regression equation of Lockhart et al. (14), using a value of 120 hours for exposure time. Values for green algae were calculated from the equation of Ellgehausen et al. (6).

Mails and Muir (19) treated an experimental pond with fenitrothion and observed that fenitrothion levels in duckweed changed relatively little from 1 to 10 days after treatment. The averages of radioactivity (as fenitrothion) in the plants over that interval were 17480 and 18229 pg/kg in shaded and sunlit ponds respectively, on a dry weight basis. During the period after treatment water content of radioactivity declined continuously, but "average" values taken as the means of initial and 10-day samples were 43 and 37 pg/L for the same ponds. Calculated bioconcentration factors were therefore 406 and 492 fold for the shaded and sunlit ponds. The rate constant ratio (Table III) indicates a steady state prediction of 24 on a wet... 

Similar to the case with fish, we are not aware of field studies with fluorene in plants. Figure 2 shows the very rapid depuration of label from duckweed in culture, resulting in the high K2 (Table III) and the short half-life (Table V). In view of the volatility of fluorene, and its short half-life it would not be expected to persist long in plants after a spray with a solvent containing fluorene. McLeese et al. (27) examined the uptake and depuration of "585 oil by mussels and found a similar result. The steady state bioconcentration factor was 160 but the half-life was only 0.3 days. 

Bioconcentration of DEHP has been observed in invertebrates, fish, and terrestrial organisms. Mean bioconcentration factors (BCFs) have been reported for algae (3,173 3,149, two species), molluscs (1,469 949, five species), Crustacea (1,164 1,182, four species), insects (1,058 772, three species), polychaetes (422, one species), fish (280 230, five species), and amphibians (605, one species) have been compiled by Staples et al. (1997). Residues of DEHP have been found in the organs of terrestrial animals such as rats, rabbits, dogs, cows, and humans (EPA 1979). However, accumulation of DEHP will be minimized by metabolism, and biomagnification of DEHP in the food chain is not expected to occur (EPA 1979 Johnson et al. 1977 Staples et al. 1997 Wofford et al. 1981). Several metabolites of DEHP might be detected in animal tissues (Johnson et al. 1977). Uptake of DEHP from soil by plants has also been reported (EPA 1986 O Connor 1996). 

The uptake of barium by fish and marine organisms is also an important removal mechanism (Bowen 1966 Schroeder 1970). Barium levels in sea water range from 2 to 63 mg/L with a mean concentration of about 13 pg/L (Bowen 1979). Barium was found to bioconcentrate in marine plants by a factor of 1,000 times the level present in the water. Bioconcentration factors in marine animals, plankton, and in brown algae of 100, 120, and 260, respectively, have been reported (Bowen 1966 Schroeder 1970). 

Transport of a contaminant from water to air is influenced primarily by wind velocity.16 The contaminant s density, vapor pressure, and aqueous solubility also factor into its tendency to be introduced into the air phase, and its Henry s constant (KH) provides a good indication of this tendency. Biota have a strong attraction to hydrophobic contaminants, and, as a result, uptake of contaminants by partitioning into plants and animals, known as bioaccumulation, has been reported to be a dominant mechanism of removal.16,25 The tendency of a chemical to be taken up into biota is quantified by the bioconcentration factor (BCF), as measured by the ratio of its concentrations in biota and water. 

---