Acceptable levels are those that do not harm humans, fish and other aquatic organisms. Carp, the fish species most sensitive to this herbicide, have been killed by Ordram (molinate). There also was the concern that people eating fish from water containing Ordram could be harmed. Bolero is toxic to aquatic organisms and also apparently causes objectionable flavors in Sacramento drinking water, even at very low concentrations.

The Department of Fish and Game, based on previous studies, recommended that Ordram concentrations in rivers and drains not exceed 90 ppb and that Bolero concentrations not exceed 24 ppb. The Department of Health Services, concerned about drinking water, recommended that Ordram and Bolero concentrations not exceed 20 and 10 ppb respectively at the intake to Sacramento's water treatment plant. Subsequent to finding that very low concentrations of Bolero apparently caused off-flavor in treated drinking water, the recommendation from Health Services was lowered to not over 1 ppb at the water intake. Regulations established by the Department of Food and Agriculture were aimed at meeting these standards without seriously impairing the rice industry.

Bolero and Ordram were added to the list of restricted materials in 1984. Their use requires a permit and filing a notice of intent with the County Agricultural Commissioner. Water was held in the rice field after Bolero and Ordram applications before releasing drainage water into the state water system. The 1984 monitoring results showed improvements over previous years. No fish kills were observed in 1984 and Ordram discharged from the Colusa Basin Drain decreased 39 percent from 1982 when a similar amount of Ordram was used. However, Ordram concentrations did exceed guidelines by the Department of Fish and Game in the Colusa Basin Drain and Reclamation District 108.

The 1985 program was designed to further decrease herbicide residues in state waters. Permitted sales of Bolero were reduced 10 percent and water management systems that maximized degradation of the herbicide were encouraged. Rice growing areas were exempt from sales limitations if they did not drain into Sacramento Valley waterways. Also exempt was land from which tailwater did not discharge into state waters for 10 days following the last Bolero application. Ordram was regulated as it was in 1984.

Results of the 1985 program were monitored through a cooperative program by the Department of Fish and Game, Central Valley Regional Water Quality Control Board and the State Water Resources Control Board. Water samples were collected regularly at different locations and analyzed in the laboratories of Chevron and Stauffer Chemical companies with quality control studies in by the Department of Fish and Game. In addition, Sacramento sampled water in and around its water treatment facility.

Figure 4 shows the analytical results from samples taken in the Sacramento River, Sacramento Slough and the Colusa Basin Drain. Maximum concentrations of molinate

 

CBD1 - Colusa Basin Drain       SS1  - Sacramento Slough       SR1  - Sacramento River at Village Marina in Sacramento County Figure 4. Ordram and Bolero concentration in water samples.

(Ordram) reached 95 ppb in late May in the Colusa Basin Drain near Knights Landing. Concentrations in the Sacramento Slough were roughly half those of the Colusa Basin Drain and were much lower in the Sacramento River. Concentrations of thiobencarb (Bolero) followed a similar pattern with respect to the three locations but at much lower levels.

Monitoring by Sacramento at the intake to its water treatment plant showed a maximum Bolero concentration of 3.7 ppb on June 3, compared with a 1.2 ppb maximum in 1984. This increase was presumed to result from a somewhat lower natural river flow, increasing the contribution from agricultural drains to the river flow. Bolero use in areas that discharge into the river was also greater.

The secondary action level for taste of drinking water set at 1.0 ppb for Bolero by the Department of Health Services was exceeded on 18 consecutive days from May 21 to June 8. Ordram level exceed the Fish and Game guidelines of 90 ppb briefly in the Colusa Basin Drain in late May but Sacramento showed a maximum of 10.6 ppb at the water intake.

Further steps are needed to reduce residues in state waters. A revised Rice Herbicide Regulatory Program for 1986 reduces Bolero sales on acreages that discharge into the Sacramento River. Areas using recirculation systems or use set-aside land to pond tail water are exempt from sales limitations. Holding time on non-exempt land is increased.

In addition to new regulations, efforts continue to inform growers of the seriousness of pesticide-laden tailwater, and use of recirculation systems is being encouraged. Enforcement activities are strengthened with emphasis on penalties for violations of labeling instructions or permit conditions.

The above summary report is bated on the draft report titled "1986 Program to Prevent Off-Site Movement of Rice Herbicides from California Rice Fields," dated October 10, 1985 and prepared by the Department of Food and Agriculture.