For the current week, the overall ratings of four chemicals stocks are worse, according to the Portfolio Graderdatabase. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Tronox Ltd. (TROX) is on the decline this week, earning a D (“sell”) after receiving a C (“hold”) last week. Tronox produces and markets titanium dioxide. In Portfolio Grader’s specific subcategories of Earnings Momentum, Earnings Revisions, Equity and Margin Growth, TROX also gets F’s. To get an in-depth look at TROX, get Portfolio Grader’s complete analysis of TROX stock.

Calgon Carbon Corporation (CCC) earns a D this week, moving down from last week’s grade of C. Calgon Carbon is engaged in products and services for purifying water and air. For more information, get Portfolio Grader’s complete analysis of CCC stock.

Marrone Bio Innovations, Inc. (MBII) earns an F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). In Earnings Momentum, Equity, Cash Flow and Sales Growth the stock gets F’s. To get an in-depth look at MBII, get Portfolio Grader’s complete analysis of MBII stock.

The rating of Rockwood Holdings, Inc. (ROC) slips from a C to a D. Rockwood Holdings is a global developer, manufacturer and marketer of value-added specialty chemicals and advanced materials used for industrial and commercial purposes. The stock gets F’s in Earnings Growth, Earnings Surprise and Margin Growth. Trade volume is up 463.6% from the previous week. For more information, get Portfolio Grader’s complete analysis of ROC stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.