Biodegradation rates

FIGURE 13.3 Possible degradation steps for an aromatic hydrocarbon. 

Initially, the cells require a period of time, the lag phase, to adjust to the altered environment. No cell multiplication occurs until the individual cells have almost doubled in size. After the adaptation is complete, the cells begin to reproduce exponentially. With each period of cell division, the population doubles. Some cells 

FIGURE 13.4 Possible degradation steps for a chlorinated hydrocarbon. 

FIGURE 13.5 Characteristic bell-shaped bacterial growth curve. 

Without renewal of the food supply, or adequate waste removal, the colony will enter the logarithmic death phase. The number of cells will decline as rapidly as it initially increased. Ultimately, the entire culture expires and the cycle is complete. 

---

Kinetics of Pesticide Biodegradation. Rates of pesticide biodegradation are important because they dictate the potential for carryover between growing seasons, contamination of surface and groundwaters, bio accumulation in macrobiota, and losses of efficacy. Pesticides are typically considered to be biodegraded via first-order kinetics, where the rate is proportional to the concentration. Figure 2 shows a typical first-order dissipation curve. 

The biodegradation rate R is characterized by the Monod (or Michaelis-Menten) following relationship ... 

Cometabohsm, which increases the biodegradation rate of the multiple targeted compounds. 

Ethoxylation of the carboxylic acid end groups of aliphatic polyesters significantly changes the biodegradation rate as well as the crystallinity of these materials (41). 

The earlier work of Miller (35), Outright (37), and Brady (5) on nonmedicated implants provided an excellent basis for further studies on specific controlled release formulations such as the determination of the biodegradation rates of lactide/glycolide drug-loaded microspheres (38). Those studies were done with l c-iabeled polymers produced from DL-lactic acid and glycolide. The final formulations tested in rats were microspheres loaded with H-labeled steroid and polymer as the matrix. The microspheres were administered intramuscularly and animals were serially sacrificed over a period of about a year. 

Experiments in rats (38) have shown that y irradiation decreases the inherent viscosity of lactide/glycolide copolymers and increases the biodegradation rate. The in vivo lifetime of a 92 8 DL-lactide/ glycolide copolymer was decreased from about 40 weeks to about 30 weeks after treatment with 2 Mrad of y irradiation. 

Yagi 0, Uchiyama H, Iwasaki K. 1992. Biodegradation rate of chloroethylene in soil environment. Water Sci Technol 25 419-424. 

Bartholomew GW, FK Pfaender (1983) Influence of spatial and temporal variations on organic pollutant biodegradation rates in an estuarine environment. Appl Environ Microbiol 45 103-109. 

A test to determine the biodegradation rate of the dispersant and the biodegradation rate of the dispersant-oil mixture has been proposed [1302]. The test method is intended to supplement the toxicity tests and the effectiveness tests, which evaluate the performance of oil spill dispersants. 

Monsanto. 1983a. TSCA sect. 8(d) submission 878211865. Santicizer 154 river die-away biodegradation rate study [microfiche 206227]. Washington, D.C. Office of Toxic Substances, U.S. Environmental Protection Agency. 

The Monod equation assumes a single carbon source. The difficulty in handling multiple carbon sources, which are typical in nature, has led to the use of an empirical biodegradation rate constant k. ... 

DBCP. The predictions suggest that DBCP is volatile and diffuses rapidly into the atmosphere and that it is also readily leached into the soil profile. In the model soil, its volatilization half-life was only 1.2 days when it was assumed to be evenly distributed into the top 10 cm of soil. However, DBCP could be leached as much as 50 cm deep by only 25 cm of water, and at this depth diffusion to the surface would be slow. From the literature study of transformation processes, we found no clear evidence for rapid oxidation or hydrolysis. Photolysis would not occur below the soil surface. No useable data for estimating biodegradation rates were found although Castro and Belser (28) showed that biodegradation did occur. The rate was assumed to be slow because all halogenated hydrocarbons degrade slowly. DBCP was therefore assumed to be persistent. 

Figure 10.17 Biodegradation rate curves for poly(vinyl alcohol) with adapted and non-adapted inoculum according to the Sapromat test [212]...

Monitoring Center and the USEPA, namely, DMP, DBP, and DOP was investigated by Wang et al. [43]. The experimental results indicated that the biodegradation rate and the biodegradability of the three phthalates under anaerobic conditions appeared to be related to the length of the alkyl-side chains. More than 90%... 

Sediment desorption t,/2 = 42.4 d from sediment under conditions mimicking marine disposal (Zhang et al. 2000). Soil biodegradation rate constant k = 0.0024 d with t,/2 = 294 d for Kidman sandy loam soil, and k = 0.0033 d with t,/2 = 211 d for McLaurin sandy loam soil (Park et al. 1990) ... 

---